End Saccheri.
Hint Resolve sac__par_strict1423 sac__par_strict1234 sac__par1423 sac__par1234
lam__par_strict1234 lam__par_strict1423 lam__par1234 lam__par1423 : Par.
Hint Resolve sac__coplanar : cop.
Section Saccheri_2D.
Context `{T2D:Tarski_2D}.

(* Specifications: *)
Lemma sac2__sac : forall A B C D E F,
Saccheri A B C D -> Saccheri A B E F -> D <> F -> Saccheri D C E F.