def innerCorner(side, fold, fatness=1, cornerMedian=MEDIAN):

    if fold == 'top':
        cornerMedian += STROKE * fatness
    if fold == 'bottom':
        cornerMedian -= STROKE * fatness

    if side == 'right':
        horHalfBar(
            side,
            median=cornerMedian,
            buttL=-1 * STROKE,
            buttR=BUTT
        )
        x = WIDTH / 2 + STROKE * fatness

    if side == 'left':
        horHalfBar(
            side,
            median=cornerMedian,
            buttL=BUTT,
            buttR=-1 * STROKE
        )
        x = WIDTH / 2 - STROKE * fatness

    if fold == 'top':
        cornerMedian -= STROKE * fatness
        vertLine(
            boxPen,
            (x, cornerMedian),
            (x, cornerMedian + HEIGHT / 2),
            STROKE * fatness,
            buttB=-1 * STROKE
        )
    if fold == 'bottom':
        cornerMedian += STROKE * fatness
        vertLine(
            boxPen,
            (x, cornerMedian - HEIGHT / 2),
            (x, cornerMedian),
            STROKE * fatness,
            buttT=-1 * STROKE
        )
Inner part of a double-stroked corner.
dataset/ETHPy150Open adobe-type-tools/box-drawing/boxDrawing.py/innerCorner