Escuadra

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    var pincel = pantalla.getContext("2d");

    pincel.fillStyle = "black";
    pincel.beginPath();
    pincel.moveTo(50,50);
    pincel.lineTo(50,400);
    pincel.lineTo(400,400);
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    pincel.fillStyle = "white";
    pincel.beginPath();
    pincel.moveTo(100,175);
    pincel.lineTo(100,350);
    pincel.lineTo(275,350);
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    pincel.fillStyle = "black";
    pincel.beginPath();
    pincel.moveTo(400,400);
    pincel.lineTo(400,50);
    pincel.lineTo(50,50);
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    pincel.fillStyle = "white";
    pincel.beginPath();
    pincel.moveTo(350,275);
    pincel.lineTo(350,100);
    pincel.lineTo(175,100);
    pincel.fill();
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