(** * Proposition 14 If with any straight line, and at a point on it, two straight lines not lying on the same side make the adjacent angles equal to two right angles, the two straight lines will be in a straight line with one another. *)
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Lemma prop_14 : forall A B C D P Q R S T U, TS A B C D -> Per P Q R ->
SumA A B C A B D S T U -> SumA P Q R P Q R S T U -> Bet C B D.