def inside_circle(cx, cy, r):
    """
    Return a function that checks whether a point is in a circle with center
    (*cx*, *cy*) and radius *r*.

    The returned function has the signature::

        f(xy: Tuple[float, float]) -> bool
    """
    r2 = r ** 2

    def _f(xy):
        x, y = xy
        return (x - cx) ** 2 + (y - cy) ** 2 < r2
    return _f