>>43
def foo(v1, v2):
____if v1.cross(v2).z < 0:
________return pi + acos(v2.dot(v1))
____else:
________return pi - acos(v2.dot(v1))

plane_angle = [0 if v2.dot(v1) < -1 else foo(v1, v2) for v1, v2 in zip(ho, ho[1:] + ho[:1])]