def share_diagonal(x0, y0, x1, y1):
    """ Is (x0, y0) on a shared diagonal with (x1, y1)? """
    dy = abs(y1 - y0)        # Calc the absolute y distance
    dx = abs(x1 - x0)        # CXalc the absolute x distance
    return dx == dy          # They clash if dx == dy