(** This is SSA congruence with a right angle *)

Lemma l11_62_unicity : forall A B C D D' P,
Coplanar A B C D -> Coplanar A B C D' ->
(forall E, Coplanar A B C E -> Per E D P) ->
(forall E, Coplanar A B C E -> Per E D' P) ->
D = D'.