(* Julien Narboux *)
(* Formalization of *)
(* Tarski's axiomatic *)
Require Export Ch07_midpoint.
Unset Regular Subst Tactic.
Definition Per := fun A B C =>
exists C', is_midpoint B C C' /\ Cong A C A C'.
Hint Resolve l8_2 : Perp.
Ltac Perp := eauto with Perp.

Lemma l8_4 : forall A B C C',
Per A B C -> is_midpoint B C C' -> Per A B C'.