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_lam2__cong_conga : forall N M P Q N' M' P' Q',
Lambert N M P Q -> Lambert N' M' P' Q' ->
Cong N Q N' Q' -> Cong P Q P' Q' ->
Cong N M N' M' /\ CongA M P Q M' P' Q'.