def vertex_saturated(v, M):
    """Determine whether a vertex is saturated by a matching.

	Parameters
	----------
	v : str (vertex key)
	M : {Edge} (set of edges)

	Return
	----------
	str / bool (relevant neighbor if saturated, False if unsaturated)
	"""
    for e in M:
        if v == e.vertices[0]:
            return e.vertices[1]
        elif v == e.vertices[1]:
            return e.vertices[0]
    return False
