Section Saccheri.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(** The two following lemmas come from Theorem 21.10 *)
(** The five following lemmas come from Theorem 21.8 *)
(** The two following lemmas constitute Theorem 21.11 *)
(** The four following constitute Theorem 22.3 *)
(** The six following lemmas constitute Theorem 22.5 *)
(** The three following lemmas constitute Omar Khayyam's Theorem (22.6) *)
(** The two following lemmas come from Theorem 22.4 *)

Lemma cong2_sac2__cong : forall A B C D A' B' C' D',
Saccheri A B C D -> Saccheri A' B' C' D' ->
Cong A B A' B' -> Cong A D A' D' ->
Cong B C B' C'.