sage: def check_prop(K,F):
....: return dual_face(K.dual(), dual_face(K,F)).is_equivalent(F)
sage: K = random_cone(max_ambient_dim=8, max_rays=10)
sage: def check_prop(K,F):
....: return dual_face(K.dual(), dual_face(K,F)).is_equivalent(F)
sage: K = random_cone(max_ambient_dim=8, max_rays=10)