<iframe 
    src="https://jsxgraph.org/share/iframe/continuity" 
    style="border: 1px solid black; overflow: hidden; width: 550px; aspect-ratio: 55 / 65;" 
    name="JSXGraph example: Continuity" 
    allowfullscreen
></iframe>

<div id="board-0-wrapper" class="jxgbox-wrapper " style="width: 100%; ">
   <div id="board-0" class="jxgbox" style="aspect-ratio: 1 / 1; width: 100%;" data-ar="1 / 1"></div>
</div>

<script type = "text/javascript"> 
    /*
    This example is licensed under a 
    Creative Commons Attribution ShareAlike 4.0 International License.
    https://creativecommons.org/licenses/by-sa/4.0/
    
    Please note you have to mention 
    The Center of Mobile Learning with Digital Technology
    in the credits.
    */
    
    const BOARDID = 'board-0';

    
    
    
    JXG.Options.text.useMathJax = true;
    JXG.Options.axis.ticks.insertTicks = false;
    JXG.Options.axis.ticks.majorHeight = 0;
    JXG.Options.axis.ticks.minorHeight = 0;
    JXG.Options.axis.ticks.drawLabels = false;
    JXG.Options.axis.ticks.insertTicks = false;
    JXG.Options.point.showInfobox = false;
    
    var board = JXG.JSXGraph.initBoard(BOARDID, {
        axis: false,
        boundingbox: [-3, 5, 5.5, -2],
        infoboxText: '',
        showCopyright: false,
        showNavigation: false,
        pan: { enabled: false },
        zoom: { enabled: false }
    });
    
    // global epsilon
    var global_epsilon = 0.00000001;
    
    /*
     * axis
     */
    
    // x-axis
    var x_axis = board.create('axis', [[0, 0], [1, 0]],
        {
            label: {
                position: 'rt',
                offset: [-10, -15]
            },
            name: '\\(x\\)',
            straightFirst: false,
            withLabel: true
        });
    
    // highlight D
    highlightElement(x_axis, "xaxis", "highlightGrey");
    
    // y-axis
    var y_axis = board.create('axis', [[0, 0], [0, 1]],
        {
            label: {
                position: 'lft',
                offset: [-40, -5]
            },
            name: '\\(f(x)\\)',
            straightFirst: false,
            withLabel: true
        });
    
    /*
     * function
     */
    
    // specific point
    var specific_point = 0;
    
    // x0 start value for glider (x0;0)
    var x0_init = 2;
    
    // function term f
    var term_f = function (x) {
        /*
         * functions
         */
    
        // continuous function (polynom)
        // return (0.25 * Math.pow(x - 2.5, 3) + 0.5 * Math.pow(x - 2.5, 2)) + 1.5;
    
        /*/ continuous function (polynom)
        specific_point = 2;
        x0_init = 3;
        return Math.pow(x - specific_point, 2) + 1;
        //*/
    
        /*/ continuous function abs()
        specific_point = 1.75;
        x0_init = 3;
        return Math.abs(x - specific_point) + 1.5;
        //*/
    
        /*/ continuous function sin()
        specific_point = 1;
        x0_init = 1.5;
        return Math.sin(2.5 * x - specific_point) + 1.5;
        //*/
    
        /*/ continuous function sin()
        x0_init = 1.8;
        return Math.sin(5 * x) / x + 2.25;
        //*/
    
        /*
         * piecewise-defined functions
         */
    
        /*/ continuous function (polynoms)
        specific_point = 2;
        x0_init = 1.5;
        if (x < specific_point) {
            return x + 1;
        } else {
            return -Math.pow((x - specific_point - 0.5), 2) + 3.25;
        }
        //*/
    
        /*/ continuous function (polynoms)
        specific_point = 2.5;
        x0_init = 1.5;
        if (x < specific_point) {
            return 1.5;
        } else {
            return Math.pow(x - specific_point, 2) + 1.5;
        }
        //*/
    
        // discontinuous function (polynoms)
        specific_point = 3.25;
        x0_init = 3.25;
        if (x < specific_point) {
            return 0.2 * x * x;
        } else {
            return x - 0.5;
        }
        //*/
    
        /*/ continuous function (polynoms)
        specific_point = Math.PI;
        x0_init = 2;
        if (x < specific_point) {
            return Math.sin(3 * x) / x + 2;
        } else {
            return -x + 2 + Math.PI;
        }
        //*/
    
    
    };
    
    // graph of f
    var graph_f = board.create('functiongraph', [term_f, 0.25, 4.1], {
        dash: 0,
        layer: 8,
        strokeColor: '#4080aa',
        strokeWidth: 2
    });
    
    // piecewise-defined discontinuous function
    if (Math.abs(term_f(specific_point - global_epsilon) - term_f(specific_point)) > global_epsilon) {
        // point (specific_point-0;f(specific_point-0))
        var point_specific_point_minus_global_epsilon_fspecific_point_minus_global_epsilon = board.create('point', [specific_point - global_epsilon, term_f(specific_point - global_epsilon)], {
            fillColor: '#ffffff',
            name: '',
            size: 1,
            strokeColor: '#4080aa',
            strokeWidth: 2
        });
    
        // point (specific_point;f(specific_point))
        var point_specific_point_fspecific_point = board.create('point', [specific_point, term_f(specific_point)], {
            fillColor: '#4080aa',
            name: '',
            size: 1,
            strokeColor: '#4080aa',
            strokeWidth: 2
        });
    
        // dashed line (specific_point;0) - (specific_point;max(f(specific_point),f(specific_point-0)))
        var line_specific_point_0_specific_point_fmax_specific_point_or_specific_point_minus_0 = board.create('line',[[specific_point,0],[specific_point,Math.max(term_f(specific_point),term_f(specific_point - global_epsilon))]],{
            dash: 1,
            name:'',
            straightFirst: false,
            straightLast: false,
            strokeColor: '#4080aa',
            strokeWidth: 1
        });
    }
    
    // highlight function
    highlightElement(graph_f, "graph", "highlightDarkBlue");
    
    /*
     * x0 and f(x0)
     */
    
    // coordonate for parallel line to x-axis
    var cx = -0.5;
    
    // start x0
    var x0_start = 0.5;
    
    // end x0
    var x0_end = 4;
    
    // line parallel to x-axis for x0 glider
    var line_parallel_x_axis = board.create('line', [[x0_start, cx], [x0_end, cx]], {
        straightFirst: false,
        straightLast: false,
        visible: false
    });
    
    // x0 glider (not on x-axis for better visibility)
    var glider_x0_0 = board.create('glider', [x0_init, 0, line_parallel_x_axis], {
        fillColor: '#ff00ff',
        label: {
            offset: [-5, -15]
        },
        name: '\\(x_0\\)',
        size: 2,
        strokeColor: '#000000',
        strokeWidth: 1
    });
    
    // highlight x0
    highlightElement(glider_x0_0, 'x0', 'highlightMagenta');
    
    // point (x0;f(x0))
    var point_x0_fx0 = board.create('point', [
        function () {
            return glider_x0_0.X();
        },
        function () {
            return term_f(glider_x0_0.X());
        }], {
        fillColor: '#000000',
        name: '',
        size: 2,
        strokeWidth: 0
    });
    
    // point (0;f(x))
    var point_0_fx0 = board.create('point', [0,
        function () {
            return term_f(glider_x0_0.X());
        }], {
        fillColor: '#000000',
        /* label not display because of epsilon
        label: {
            offset: [-45, 0]
        },
        name: '\\(f(x_0)\\)',
        */
        name: '',
        size: 2,
        strokeWidth: 0
    });
    
    // dashed line (x0;0) - (x0;f(x0))
    var line_x0_0_x0_fx0 = board.create('line', [glider_x0_0, point_x0_fx0], {
        dash: 2,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#000000',
        strokeWidth: 1,
    });
    
    // point (x0;0) on x-axis (refers to glider_x0_0)
    var point_x0_0 = board.create('intersection', [x_axis, line_x0_0_x0_fx0], {
        fillColor: '#000000',
        label: {
            offset: [-20, -35]
        },
        name: '',
        size: 1,
        strokeWidth: 0
    });
    
    // dashed line (x0;f(x0)) - (0;f(x0))
    var line_x0_fx0_0_fx0 = board.create('line', [point_x0_fx0, point_0_fx0], {
        dash: 2,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#000000',
        strokeWidth: 1,
    });
    
    /*
     * epsilon
     */
    
    // coordonate for parallel line to y-axis
    var cx = -1.1;
    
    // point (cx;f(x0))
    var point_cx_fx0 = board.create('point', [function () {
        return point_0_fx0.X() + cx;
    
    }, function () {
        return point_0_fx0.Y();
    }], {
        fillColor: '#000000',
        label: {
            offset: [-55, 0]
        },
        name: '\\(f(x_0)\\)',
        size: 2,
        strokeWidth: 0
    });
    
    // point (cx,f(x0)+1)
    var point_cx_fx01 = board.create('point', [function () {
        return point_cx_fx0.X();
    
    }, function () {
        return point_cx_fx0.Y() + 1;
    }], {
        visible: false
    });
    
    // dashed line (0;f(x0)) - (cx;f(x0))
    var line_0_fx0_cx_fx0 = board.create('line', [point_0_fx0, point_cx_fx0], {
        dash: 2,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#000000',
        strokeWidth: 1
    });
    
    // line (cx;f(x0)) - (cx,f(x0)+1) for epsilon glider
    var line_cx_fx0_cx_fx01 = board.create('line', [point_cx_fx0, point_cx_fx01], {
        straightFirst: false,
        visible: false
    });
    
    // epsilon
    var epsilon = 1;
    
    // epsilon glider
    var glider_cx_fx0_espilon = board.create('glider', [0, (function () {
        return point_0_fx0.Y() + epsilon;
    })(), line_cx_fx0_cx_fx01], {
        fillColor: '#00dd66',
        label: {
            offset: [-55, 20]
        },
        name: '\\(f(x_0)+\\epsilon\\)',
        size: 2,
        strokeColor: '#000000',
        strokeWidth: 1
    });
    
    // highlight epsilon point
    highlightElement(glider_cx_fx0_espilon, "epsilon", "highlightGreen");
    
    // epsilon as line length
    var line_cx_fx0_cx_fx0_epsilon = board.create('line', [point_cx_fx0, glider_cx_fx0_espilon], {
        straightFirst: false,
        straightLast: false,
        strokeColor: '#00dd66',
        strokeWidth: 3
    });
    
    // highlight epsilon line
    highlightElement(line_cx_fx0_cx_fx0_epsilon, "epsilon", "highlightGreen");
    
    // point for epsilon label
    var point_label_epsilon = board.create('midpoint', [point_cx_fx0, glider_cx_fx0_espilon], {
        label: {
            offset: [5, 1]
        },
        name: '\\(\\epsilon\\)',
        size: 0
    });
    
    // point (cx;f(x0)-epsilon)
    var point_cx_fx0_minus_epsilon = board.create('mirrorpoint', [glider_cx_fx0_espilon, point_cx_fx0], {
        fillColor: '#000000',
        label: {
            offset: [-55, -20]
        },
        name: '\\(f(x_0)-\\epsilon\\)',
        size: 2,
        strokeWidth: 0
    });
    
    // dotted line (cx;f(x0)) - (cx;f(x0)-epsilon)
    var line_cx_fx0_cx_fx0_minus_epsilon = board.create('line', [point_cx_fx0, point_cx_fx0_minus_epsilon], {
        dash: 1,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#00dd66'
    });
    
    // point (0,f(x0)+epsilon)
    var point_0_fx0_epsilon = board.create('point', [0,
        function () {
            return glider_cx_fx0_espilon.Y();
        }], {
        fillColor: '#000000',
        name: '',
        size: 1,
        strokeWidth: 0
    });
    
    // point (0,f(x0)-epsilon)
    var point_0_fx0_minus_epsilon = board.create('point', [0,
        function () {
            return point_cx_fx0_minus_epsilon.Y();
        }], {
        fillColor: '#000000',
        name: '',
        size: 1,
        strokeWidth: 0
    });
    
    // line (cx;f(x0)+epsilon) - (0;f(x0)+epsilon)
    var line_cx_fx0_epsilon_0_fx0_epsilon = board.create('line', [glider_cx_fx0_espilon, point_0_fx0_epsilon], {
        dash: 1,
        straightFirst: false,
        straightLast: true,
        strokeColor: '#cccccc'
    });
    
    // line (cx;f(x0)-epsilon) - (0;f(x0)-epsilon)
    var line_cx_fx0_minus_epsilon_0_fx0_minus_epsilon = board.create('line', [point_cx_fx0_minus_epsilon, point_0_fx0_minus_epsilon], {
        dash: 1,
        straightFirst: false,
        straightLast: true,
        strokeColor: '#cccccc'
    });
    
    /*
     * delta
     */
    
    // coordonate for parallel line to x-axis
    var cy = -1.25;
    
    // point (x0;cy)
    var point_x0_cy = board.create('point', [function () {
        return glider_x0_0.X();
    }, cy], {
        fillColor: '#000000',
        name: '',
        size: 2,
        strokeWidth: 0
    });
    
    // point (x0+1;cy)
    var point_x01_cy = board.create('point', [function () {
        return glider_x0_0.X() + 1;
    
    }, cy], {
        visible: false
    });
    
    // line (x0;cy) - (x0+1,cy) for delta glider
    var line_x0_cy_x01_cy = board.create('line', [point_x0_cy, point_x01_cy], {
        straightFirst: false,
        visible: false
    });
    
    // delta
    var delta = 0.75;
    
    // delta glider
    var glider_x0_delta_cy = board.create('glider', [(function () {
        return point_x0_0.X() + delta;
    })(), cy, line_x0_cy_x01_cy], {
        fillColor: '#ffaa33',
        label: {
            offset: [10, -10]
        },
        name: '\\(x_0+\\delta\\)',
        size: 2,
        strokeColor: '#000000',
        strokeWidth: 1
    });
    
    // highlight delta point
    highlightElement(glider_x0_delta_cy, "delta", "highlightOrange");
    
    // delta as line length
    var line_x0_cy_x0_delta_cy = board.create('line', [point_x0_cy, glider_x0_delta_cy], {
        straightFirst: false,
        straightLast: false,
        strokeColor: '#ffaa33',
        strokeWidth: 3
    });
    
    // highlight delta line
    highlightElement(line_x0_cy_x0_delta_cy, "delta", "highlightOrange");
    
    // point (x0-delta;cy)
    var point_x0_minus_delta_cy = board.create('mirrorpoint', [glider_x0_delta_cy, point_x0_cy], {
        fillColor: '#000000',
        label: {
            offset: [-50, -10]
        },
        name: '\\(x_0-\\delta\\)',
        size: 2,
        strokeWidth: 0
    });
    
    // dotted line (x0;cy) - (x0-delta;cy)
    var line_x0_cy_x0_minus_delta_cy = board.create('line', [point_x0_cy, point_x0_minus_delta_cy], {
        dash: 1,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#ffaa33'
    });
    
    // point for delta label
    var point_label_delta = board.create('midpoint', [point_x0_cy, glider_x0_delta_cy], {
        label: {
            offset: [-2, 12]
        },
        name: '\\(\\delta\\)',
        size: 0
    });
    
    // point (x0+delta;0)
    var point_x0_delta_0 = board.create('point', [
        function () {
            return glider_x0_delta_cy.X();
        }, 0], {
        fillColor: '#000000',
        label: {
            offset: [-20, -35]
        },
        name: '',
        size: 1,
        strokeWidth: 0
    });
    
    // point (x0-delta;0)
    var point_x0_minus_delta_0 = board.create('point', [
        function () {
            return point_x0_minus_delta_cy.X();
        }, 0], {
        fillColor: '#000000',
        label: {
            offset: [-20, -35]
        },
        name: '',
        size: 1,
        strokeWidth: 0
    });
    
    // end point y for vertical dotted line
    var cym = 4.75;
    
    // point (x0+delta;cym)
    var point_x0_delta_cym = board.create('point', [
        function () {
            return glider_x0_delta_cy.X();
        }, cym], {
        visible: false
    });
    
    // point (x0-delta;cym)
    var point_x0_minus_delta_cym = board.create('point', [
        function () {
            return point_x0_minus_delta_cy.X();
        }, cym], {
        visible: false
    });
    
    // dotted line (x0+delta;cy) - (x0+delta;cym)
    var line_x0_delta_cy_x0_delta_cym = board.create('line', [glider_x0_delta_cy, point_x0_delta_cym], {
        dash: 1,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#cccccc'
    });
    
    // dotted line (x0-delta;cy) - (x0-delta;cym)
    var line_x0_minus_delta_cy_x0_minus_delta_cym = board.create('line', [point_x0_minus_delta_cy, point_x0_minus_delta_cym], {
        dash: 1,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#cccccc'
    });
    
    /*
     * intersections delta an epsilon lines
     */
    
    // point (x0+delta;f(x0)+epsilon)
    var point_x0_delta_fx0_epsilon = board.create('intersection', [line_x0_delta_cy_x0_delta_cym, line_cx_fx0_epsilon_0_fx0_epsilon, 0], {
        fillColor: '#000000',
        name: '',
        size: 1,
        strokeWidth: 0
    });
    
    // point (x0-delta;f(x0)+epsilon)
    var point_x0_minus_delta_fx0_epsilon = board.create('intersection', [line_x0_minus_delta_cy_x0_minus_delta_cym, line_cx_fx0_epsilon_0_fx0_epsilon, 0], {
        fillColor: '#000000',
        name: '',
        size: 1,
        strokeWidth: 0
    });
    // point (x0+delta;f(x0)-epsilon)
    var point_x0_delta_fx0_epsilon = board.create('intersection', [line_x0_delta_cy_x0_delta_cym, line_cx_fx0_minus_epsilon_0_fx0_minus_epsilon, 0], {
        fillColor: '#000000',
        name: '',
        size: 1,
        strokeWidth: 0
    });
    // point (x0+delta;f(x0)+epsilon)
    var point_x0_delta_fx0_epsilon = board.create('intersection', [line_x0_minus_delta_cy_x0_minus_delta_cym, line_cx_fx0_minus_epsilon_0_fx0_minus_epsilon, 0], {
        fillColor: '#000000',
        name: '',
        size: 1,
        strokeWidth: 0
    });
    
    /*
     * x
     */
    
    // line (x0-delta;0) - (x0+delta;0) for x glider
    var line_x0_minus_delta_0_x0_delta_0 = board.create('line', [point_x0_minus_delta_0, point_x0_delta_0], {
        straightFirst: false,
        straightLast: false,
        visible: false
    });
    
    // x glider
    var glider_x_0 = board.create('glider', [glider_x0_0.X() + delta / 2, 0, line_x0_minus_delta_0_x0_delta_0], {
        fillColor: '#3366ff',
        label: {
            offset: [-4, -15]
        },
        name: '\\(x\\)',
        size: 2,
        strokeColor: '#000000',
        strokeWidth: 1
    });
    
    // highlight x
    highlightElement(glider_x_0, 'xed', 'highlightBlue');
    
    // point (x;f(x))
    var point_x_fx = board.create('point', [
        function () {
            return glider_x_0.X();
        },
        function () {
            return term_f(glider_x_0.X());
        }], {
        fillColor: '#000000',
        name: '',
        size: 2,
        strokeWidth: 0
    });
    
    // point (0;f(x))
    var point_0_fx = board.create('point', [0,
        function () {
            return term_f(glider_x_0.X());
        }], {
        fillColor: '#000000',
        label: {
            offset: [-30, 0]
        },
        name: '\\(f(x)\\)',
        size: 2,
        strokeWidth: 0
    });
    
    // dotted line (x;0) -(x,f(x))
    var line_x_0_x_fx = board.create('line', [glider_x_0, point_x_fx], {
        dash: 2,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#000000',
        strokeWidth: 1,
    });
    
    // dotted line (x;f(x)) - (0;f(x))
    var line_x_fx_0_fx = board.create('line', [point_x_fx, point_0_fx], {
        dash: 2,
        straightFirst: false,
        straightLast: false,
        strokeColor: '#000000',
        strokeWidth: 1,
    });
    
    /*
     * line  for |x-x0|<delta
     */
    
    // line (x0;0) - (x;0) for |x-x0|<delta
    var line_x0_0_x_0 = board.create('line', [point_x0_0, glider_x_0], {
        straightFirst: false,
        straightLast: false,
        strokeColor: '#3366ff',
        strokeWidth: 3,
    });
    
    // highlight |x-x0|<delta
    highlightElement(line_x0_0_x_0, 'xx0d', 'highlightBlue');
    
    /*
     * line  for |f(x)-f(x0)|<epsilon
     */
    
    // line (0;f(x)) - (0;f(x0)) for |f(x)-f(x0)|<epsilon with epsilon-delta-condition
    var line_0_fx_0_fx0 = board.create('line', [point_0_fx0, point_0_fx], {
        straightFirst: false,
        straightLast: false,
        strokeColor: function () {
            if (line_cx_fx0_cx_fx0_epsilon.L() > point_0_fx0.Dist(point_0_fx))
                return '#993333';
            else
                return '#ff00ff';
        },
        strokeWidth: 3,
    });
    
    // highlight |f(x)-f(x0)|<epsilon
    highlightElement(line_0_fx_0_fx0, 'fxfx0', 'highlightDarkRed');
    
    // area with epsilon-delta-condition
    var polygon_delta_epsilon = board.create('polygon', [
        point_x0_0,
        glider_x_0,
        point_x_fx,
        point_0_fx,
        point_0_fx0,
        point_x0_fx0
    ], {
        borders: {
            visible: false
        },
        fillColor: function () {
            if (line_cx_fx0_cx_fx0_epsilon.L() > point_0_fx0.Dist(point_0_fx))
                return '#dddddd';
            else
                return '#ff00ff';
        },
        highlightFillColor: '#dddddd'
    });
    
    /*
     * alert epsilon-delta-condition
     */
    
    function highlightElement(el, id, cl) {
    
    }
    
 </script> 

<jsxgraph width="100%" aspect-ratio="1 / 1" title="Continuity" description="This construction was copied from JSXGraph examples database: BTW HERE SHOULD BE A GENERATED LINKuseGlobalJS="false">
   /*
   This example is licensed under a 
   Creative Commons Attribution ShareAlike 4.0 International License.
   https://creativecommons.org/licenses/by-sa/4.0/
   
   Please note you have to mention 
   The Center of Mobile Learning with Digital Technology
   in the credits.
   */
   
   
   
   
   JXG.Options.text.useMathJax = true;
   JXG.Options.axis.ticks.insertTicks = false;
   JXG.Options.axis.ticks.majorHeight = 0;
   JXG.Options.axis.ticks.minorHeight = 0;
   JXG.Options.axis.ticks.drawLabels = false;
   JXG.Options.axis.ticks.insertTicks = false;
   JXG.Options.point.showInfobox = false;
   
   var board = JXG.JSXGraph.initBoard(BOARDID, {
       axis: false,
       boundingbox: [-3, 5, 5.5, -2],
       infoboxText: '',
       showCopyright: false,
       showNavigation: false,
       pan: { enabled: false },
       zoom: { enabled: false }
   });
   
   // global epsilon
   var global_epsilon = 0.00000001;
   
   /*
    * axis
    */
   
   // x-axis
   var x_axis = board.create('axis', [[0, 0], [1, 0]],
       {
           label: {
               position: 'rt',
               offset: [-10, -15]
           },
           name: '\\(x\\)',
           straightFirst: false,
           withLabel: true
       });
   
   // highlight D
   highlightElement(x_axis, "xaxis", "highlightGrey");
   
   // y-axis
   var y_axis = board.create('axis', [[0, 0], [0, 1]],
       {
           label: {
               position: 'lft',
               offset: [-40, -5]
           },
           name: '\\(f(x)\\)',
           straightFirst: false,
           withLabel: true
       });
   
   /*
    * function
    */
   
   // specific point
   var specific_point = 0;
   
   // x0 start value for glider (x0;0)
   var x0_init = 2;
   
   // function term f
   var term_f = function (x) {
       /*
        * functions
        */
   
       // continuous function (polynom)
       // return (0.25 * Math.pow(x - 2.5, 3) + 0.5 * Math.pow(x - 2.5, 2)) + 1.5;
   
       /*/ continuous function (polynom)
       specific_point = 2;
       x0_init = 3;
       return Math.pow(x - specific_point, 2) + 1;
       //*/
   
       /*/ continuous function abs()
       specific_point = 1.75;
       x0_init = 3;
       return Math.abs(x - specific_point) + 1.5;
       //*/
   
       /*/ continuous function sin()
       specific_point = 1;
       x0_init = 1.5;
       return Math.sin(2.5 * x - specific_point) + 1.5;
       //*/
   
       /*/ continuous function sin()
       x0_init = 1.8;
       return Math.sin(5 * x) / x + 2.25;
       //*/
   
       /*
        * piecewise-defined functions
        */
   
       /*/ continuous function (polynoms)
       specific_point = 2;
       x0_init = 1.5;
       if (x < specific_point) {
           return x + 1;
       } else {
           return -Math.pow((x - specific_point - 0.5), 2) + 3.25;
       }
       //*/
   
       /*/ continuous function (polynoms)
       specific_point = 2.5;
       x0_init = 1.5;
       if (x < specific_point) {
           return 1.5;
       } else {
           return Math.pow(x - specific_point, 2) + 1.5;
       }
       //*/
   
       // discontinuous function (polynoms)
       specific_point = 3.25;
       x0_init = 3.25;
       if (x < specific_point) {
           return 0.2 * x * x;
       } else {
           return x - 0.5;
       }
       //*/
   
       /*/ continuous function (polynoms)
       specific_point = Math.PI;
       x0_init = 2;
       if (x < specific_point) {
           return Math.sin(3 * x) / x + 2;
       } else {
           return -x + 2 + Math.PI;
       }
       //*/
   
   
   };
   
   // graph of f
   var graph_f = board.create('functiongraph', [term_f, 0.25, 4.1], {
       dash: 0,
       layer: 8,
       strokeColor: '#4080aa',
       strokeWidth: 2
   });
   
   // piecewise-defined discontinuous function
   if (Math.abs(term_f(specific_point - global_epsilon) - term_f(specific_point)) > global_epsilon) {
       // point (specific_point-0;f(specific_point-0))
       var point_specific_point_minus_global_epsilon_fspecific_point_minus_global_epsilon = board.create('point', [specific_point - global_epsilon, term_f(specific_point - global_epsilon)], {
           fillColor: '#ffffff',
           name: '',
           size: 1,
           strokeColor: '#4080aa',
           strokeWidth: 2
       });
   
       // point (specific_point;f(specific_point))
       var point_specific_point_fspecific_point = board.create('point', [specific_point, term_f(specific_point)], {
           fillColor: '#4080aa',
           name: '',
           size: 1,
           strokeColor: '#4080aa',
           strokeWidth: 2
       });
   
       // dashed line (specific_point;0) - (specific_point;max(f(specific_point),f(specific_point-0)))
       var line_specific_point_0_specific_point_fmax_specific_point_or_specific_point_minus_0 = board.create('line',[[specific_point,0],[specific_point,Math.max(term_f(specific_point),term_f(specific_point - global_epsilon))]],{
           dash: 1,
           name:'',
           straightFirst: false,
           straightLast: false,
           strokeColor: '#4080aa',
           strokeWidth: 1
       });
   }
   
   // highlight function
   highlightElement(graph_f, "graph", "highlightDarkBlue");
   
   /*
    * x0 and f(x0)
    */
   
   // coordonate for parallel line to x-axis
   var cx = -0.5;
   
   // start x0
   var x0_start = 0.5;
   
   // end x0
   var x0_end = 4;
   
   // line parallel to x-axis for x0 glider
   var line_parallel_x_axis = board.create('line', [[x0_start, cx], [x0_end, cx]], {
       straightFirst: false,
       straightLast: false,
       visible: false
   });
   
   // x0 glider (not on x-axis for better visibility)
   var glider_x0_0 = board.create('glider', [x0_init, 0, line_parallel_x_axis], {
       fillColor: '#ff00ff',
       label: {
           offset: [-5, -15]
       },
       name: '\\(x_0\\)',
       size: 2,
       strokeColor: '#000000',
       strokeWidth: 1
   });
   
   // highlight x0
   highlightElement(glider_x0_0, 'x0', 'highlightMagenta');
   
   // point (x0;f(x0))
   var point_x0_fx0 = board.create('point', [
       function () {
           return glider_x0_0.X();
       },
       function () {
           return term_f(glider_x0_0.X());
       }], {
       fillColor: '#000000',
       name: '',
       size: 2,
       strokeWidth: 0
   });
   
   // point (0;f(x))
   var point_0_fx0 = board.create('point', [0,
       function () {
           return term_f(glider_x0_0.X());
       }], {
       fillColor: '#000000',
       /* label not display because of epsilon
       label: {
           offset: [-45, 0]
       },
       name: '\\(f(x_0)\\)',
       */
       name: '',
       size: 2,
       strokeWidth: 0
   });
   
   // dashed line (x0;0) - (x0;f(x0))
   var line_x0_0_x0_fx0 = board.create('line', [glider_x0_0, point_x0_fx0], {
       dash: 2,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#000000',
       strokeWidth: 1,
   });
   
   // point (x0;0) on x-axis (refers to glider_x0_0)
   var point_x0_0 = board.create('intersection', [x_axis, line_x0_0_x0_fx0], {
       fillColor: '#000000',
       label: {
           offset: [-20, -35]
       },
       name: '',
       size: 1,
       strokeWidth: 0
   });
   
   // dashed line (x0;f(x0)) - (0;f(x0))
   var line_x0_fx0_0_fx0 = board.create('line', [point_x0_fx0, point_0_fx0], {
       dash: 2,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#000000',
       strokeWidth: 1,
   });
   
   /*
    * epsilon
    */
   
   // coordonate for parallel line to y-axis
   var cx = -1.1;
   
   // point (cx;f(x0))
   var point_cx_fx0 = board.create('point', [function () {
       return point_0_fx0.X() + cx;
   
   }, function () {
       return point_0_fx0.Y();
   }], {
       fillColor: '#000000',
       label: {
           offset: [-55, 0]
       },
       name: '\\(f(x_0)\\)',
       size: 2,
       strokeWidth: 0
   });
   
   // point (cx,f(x0)+1)
   var point_cx_fx01 = board.create('point', [function () {
       return point_cx_fx0.X();
   
   }, function () {
       return point_cx_fx0.Y() + 1;
   }], {
       visible: false
   });
   
   // dashed line (0;f(x0)) - (cx;f(x0))
   var line_0_fx0_cx_fx0 = board.create('line', [point_0_fx0, point_cx_fx0], {
       dash: 2,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#000000',
       strokeWidth: 1
   });
   
   // line (cx;f(x0)) - (cx,f(x0)+1) for epsilon glider
   var line_cx_fx0_cx_fx01 = board.create('line', [point_cx_fx0, point_cx_fx01], {
       straightFirst: false,
       visible: false
   });
   
   // epsilon
   var epsilon = 1;
   
   // epsilon glider
   var glider_cx_fx0_espilon = board.create('glider', [0, (function () {
       return point_0_fx0.Y() + epsilon;
   })(), line_cx_fx0_cx_fx01], {
       fillColor: '#00dd66',
       label: {
           offset: [-55, 20]
       },
       name: '\\(f(x_0)+\\epsilon\\)',
       size: 2,
       strokeColor: '#000000',
       strokeWidth: 1
   });
   
   // highlight epsilon point
   highlightElement(glider_cx_fx0_espilon, "epsilon", "highlightGreen");
   
   // epsilon as line length
   var line_cx_fx0_cx_fx0_epsilon = board.create('line', [point_cx_fx0, glider_cx_fx0_espilon], {
       straightFirst: false,
       straightLast: false,
       strokeColor: '#00dd66',
       strokeWidth: 3
   });
   
   // highlight epsilon line
   highlightElement(line_cx_fx0_cx_fx0_epsilon, "epsilon", "highlightGreen");
   
   // point for epsilon label
   var point_label_epsilon = board.create('midpoint', [point_cx_fx0, glider_cx_fx0_espilon], {
       label: {
           offset: [5, 1]
       },
       name: '\\(\\epsilon\\)',
       size: 0
   });
   
   // point (cx;f(x0)-epsilon)
   var point_cx_fx0_minus_epsilon = board.create('mirrorpoint', [glider_cx_fx0_espilon, point_cx_fx0], {
       fillColor: '#000000',
       label: {
           offset: [-55, -20]
       },
       name: '\\(f(x_0)-\\epsilon\\)',
       size: 2,
       strokeWidth: 0
   });
   
   // dotted line (cx;f(x0)) - (cx;f(x0)-epsilon)
   var line_cx_fx0_cx_fx0_minus_epsilon = board.create('line', [point_cx_fx0, point_cx_fx0_minus_epsilon], {
       dash: 1,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#00dd66'
   });
   
   // point (0,f(x0)+epsilon)
   var point_0_fx0_epsilon = board.create('point', [0,
       function () {
           return glider_cx_fx0_espilon.Y();
       }], {
       fillColor: '#000000',
       name: '',
       size: 1,
       strokeWidth: 0
   });
   
   // point (0,f(x0)-epsilon)
   var point_0_fx0_minus_epsilon = board.create('point', [0,
       function () {
           return point_cx_fx0_minus_epsilon.Y();
       }], {
       fillColor: '#000000',
       name: '',
       size: 1,
       strokeWidth: 0
   });
   
   // line (cx;f(x0)+epsilon) - (0;f(x0)+epsilon)
   var line_cx_fx0_epsilon_0_fx0_epsilon = board.create('line', [glider_cx_fx0_espilon, point_0_fx0_epsilon], {
       dash: 1,
       straightFirst: false,
       straightLast: true,
       strokeColor: '#cccccc'
   });
   
   // line (cx;f(x0)-epsilon) - (0;f(x0)-epsilon)
   var line_cx_fx0_minus_epsilon_0_fx0_minus_epsilon = board.create('line', [point_cx_fx0_minus_epsilon, point_0_fx0_minus_epsilon], {
       dash: 1,
       straightFirst: false,
       straightLast: true,
       strokeColor: '#cccccc'
   });
   
   /*
    * delta
    */
   
   // coordonate for parallel line to x-axis
   var cy = -1.25;
   
   // point (x0;cy)
   var point_x0_cy = board.create('point', [function () {
       return glider_x0_0.X();
   }, cy], {
       fillColor: '#000000',
       name: '',
       size: 2,
       strokeWidth: 0
   });
   
   // point (x0+1;cy)
   var point_x01_cy = board.create('point', [function () {
       return glider_x0_0.X() + 1;
   
   }, cy], {
       visible: false
   });
   
   // line (x0;cy) - (x0+1,cy) for delta glider
   var line_x0_cy_x01_cy = board.create('line', [point_x0_cy, point_x01_cy], {
       straightFirst: false,
       visible: false
   });
   
   // delta
   var delta = 0.75;
   
   // delta glider
   var glider_x0_delta_cy = board.create('glider', [(function () {
       return point_x0_0.X() + delta;
   })(), cy, line_x0_cy_x01_cy], {
       fillColor: '#ffaa33',
       label: {
           offset: [10, -10]
       },
       name: '\\(x_0+\\delta\\)',
       size: 2,
       strokeColor: '#000000',
       strokeWidth: 1
   });
   
   // highlight delta point
   highlightElement(glider_x0_delta_cy, "delta", "highlightOrange");
   
   // delta as line length
   var line_x0_cy_x0_delta_cy = board.create('line', [point_x0_cy, glider_x0_delta_cy], {
       straightFirst: false,
       straightLast: false,
       strokeColor: '#ffaa33',
       strokeWidth: 3
   });
   
   // highlight delta line
   highlightElement(line_x0_cy_x0_delta_cy, "delta", "highlightOrange");
   
   // point (x0-delta;cy)
   var point_x0_minus_delta_cy = board.create('mirrorpoint', [glider_x0_delta_cy, point_x0_cy], {
       fillColor: '#000000',
       label: {
           offset: [-50, -10]
       },
       name: '\\(x_0-\\delta\\)',
       size: 2,
       strokeWidth: 0
   });
   
   // dotted line (x0;cy) - (x0-delta;cy)
   var line_x0_cy_x0_minus_delta_cy = board.create('line', [point_x0_cy, point_x0_minus_delta_cy], {
       dash: 1,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#ffaa33'
   });
   
   // point for delta label
   var point_label_delta = board.create('midpoint', [point_x0_cy, glider_x0_delta_cy], {
       label: {
           offset: [-2, 12]
       },
       name: '\\(\\delta\\)',
       size: 0
   });
   
   // point (x0+delta;0)
   var point_x0_delta_0 = board.create('point', [
       function () {
           return glider_x0_delta_cy.X();
       }, 0], {
       fillColor: '#000000',
       label: {
           offset: [-20, -35]
       },
       name: '',
       size: 1,
       strokeWidth: 0
   });
   
   // point (x0-delta;0)
   var point_x0_minus_delta_0 = board.create('point', [
       function () {
           return point_x0_minus_delta_cy.X();
       }, 0], {
       fillColor: '#000000',
       label: {
           offset: [-20, -35]
       },
       name: '',
       size: 1,
       strokeWidth: 0
   });
   
   // end point y for vertical dotted line
   var cym = 4.75;
   
   // point (x0+delta;cym)
   var point_x0_delta_cym = board.create('point', [
       function () {
           return glider_x0_delta_cy.X();
       }, cym], {
       visible: false
   });
   
   // point (x0-delta;cym)
   var point_x0_minus_delta_cym = board.create('point', [
       function () {
           return point_x0_minus_delta_cy.X();
       }, cym], {
       visible: false
   });
   
   // dotted line (x0+delta;cy) - (x0+delta;cym)
   var line_x0_delta_cy_x0_delta_cym = board.create('line', [glider_x0_delta_cy, point_x0_delta_cym], {
       dash: 1,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#cccccc'
   });
   
   // dotted line (x0-delta;cy) - (x0-delta;cym)
   var line_x0_minus_delta_cy_x0_minus_delta_cym = board.create('line', [point_x0_minus_delta_cy, point_x0_minus_delta_cym], {
       dash: 1,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#cccccc'
   });
   
   /*
    * intersections delta an epsilon lines
    */
   
   // point (x0+delta;f(x0)+epsilon)
   var point_x0_delta_fx0_epsilon = board.create('intersection', [line_x0_delta_cy_x0_delta_cym, line_cx_fx0_epsilon_0_fx0_epsilon, 0], {
       fillColor: '#000000',
       name: '',
       size: 1,
       strokeWidth: 0
   });
   
   // point (x0-delta;f(x0)+epsilon)
   var point_x0_minus_delta_fx0_epsilon = board.create('intersection', [line_x0_minus_delta_cy_x0_minus_delta_cym, line_cx_fx0_epsilon_0_fx0_epsilon, 0], {
       fillColor: '#000000',
       name: '',
       size: 1,
       strokeWidth: 0
   });
   // point (x0+delta;f(x0)-epsilon)
   var point_x0_delta_fx0_epsilon = board.create('intersection', [line_x0_delta_cy_x0_delta_cym, line_cx_fx0_minus_epsilon_0_fx0_minus_epsilon, 0], {
       fillColor: '#000000',
       name: '',
       size: 1,
       strokeWidth: 0
   });
   // point (x0+delta;f(x0)+epsilon)
   var point_x0_delta_fx0_epsilon = board.create('intersection', [line_x0_minus_delta_cy_x0_minus_delta_cym, line_cx_fx0_minus_epsilon_0_fx0_minus_epsilon, 0], {
       fillColor: '#000000',
       name: '',
       size: 1,
       strokeWidth: 0
   });
   
   /*
    * x
    */
   
   // line (x0-delta;0) - (x0+delta;0) for x glider
   var line_x0_minus_delta_0_x0_delta_0 = board.create('line', [point_x0_minus_delta_0, point_x0_delta_0], {
       straightFirst: false,
       straightLast: false,
       visible: false
   });
   
   // x glider
   var glider_x_0 = board.create('glider', [glider_x0_0.X() + delta / 2, 0, line_x0_minus_delta_0_x0_delta_0], {
       fillColor: '#3366ff',
       label: {
           offset: [-4, -15]
       },
       name: '\\(x\\)',
       size: 2,
       strokeColor: '#000000',
       strokeWidth: 1
   });
   
   // highlight x
   highlightElement(glider_x_0, 'xed', 'highlightBlue');
   
   // point (x;f(x))
   var point_x_fx = board.create('point', [
       function () {
           return glider_x_0.X();
       },
       function () {
           return term_f(glider_x_0.X());
       }], {
       fillColor: '#000000',
       name: '',
       size: 2,
       strokeWidth: 0
   });
   
   // point (0;f(x))
   var point_0_fx = board.create('point', [0,
       function () {
           return term_f(glider_x_0.X());
       }], {
       fillColor: '#000000',
       label: {
           offset: [-30, 0]
       },
       name: '\\(f(x)\\)',
       size: 2,
       strokeWidth: 0
   });
   
   // dotted line (x;0) -(x,f(x))
   var line_x_0_x_fx = board.create('line', [glider_x_0, point_x_fx], {
       dash: 2,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#000000',
       strokeWidth: 1,
   });
   
   // dotted line (x;f(x)) - (0;f(x))
   var line_x_fx_0_fx = board.create('line', [point_x_fx, point_0_fx], {
       dash: 2,
       straightFirst: false,
       straightLast: false,
       strokeColor: '#000000',
       strokeWidth: 1,
   });
   
   /*
    * line  for |x-x0|<delta
    */
   
   // line (x0;0) - (x;0) for |x-x0|<delta
   var line_x0_0_x_0 = board.create('line', [point_x0_0, glider_x_0], {
       straightFirst: false,
       straightLast: false,
       strokeColor: '#3366ff',
       strokeWidth: 3,
   });
   
   // highlight |x-x0|<delta
   highlightElement(line_x0_0_x_0, 'xx0d', 'highlightBlue');
   
   /*
    * line  for |f(x)-f(x0)|<epsilon
    */
   
   // line (0;f(x)) - (0;f(x0)) for |f(x)-f(x0)|<epsilon with epsilon-delta-condition
   var line_0_fx_0_fx0 = board.create('line', [point_0_fx0, point_0_fx], {
       straightFirst: false,
       straightLast: false,
       strokeColor: function () {
           if (line_cx_fx0_cx_fx0_epsilon.L() > point_0_fx0.Dist(point_0_fx))
               return '#993333';
           else
               return '#ff00ff';
       },
       strokeWidth: 3,
   });
   
   // highlight |f(x)-f(x0)|<epsilon
   highlightElement(line_0_fx_0_fx0, 'fxfx0', 'highlightDarkRed');
   
   // area with epsilon-delta-condition
   var polygon_delta_epsilon = board.create('polygon', [
       point_x0_0,
       glider_x_0,
       point_x_fx,
       point_0_fx,
       point_0_fx0,
       point_x0_fx0
   ], {
       borders: {
           visible: false
       },
       fillColor: function () {
           if (line_cx_fx0_cx_fx0_epsilon.L() > point_0_fx0.Dist(point_0_fx))
               return '#dddddd';
           else
               return '#ff00ff';
       },
       highlightFillColor: '#dddddd'
   });
   
   /*
    * alert epsilon-delta-condition
    */
   
   function highlightElement(el, id, cl) {
   
   }
   
</jsxgraph>