(* Julien Narboux *)
(* Formalization of *)
(* Tarski's axiomatic *)
Require Export Ch06_out_lines.
Unset Regular Subst Tactic.
Definition is_midpoint := fun M A B => Bet A M B /\ Cong A M M B.

Lemma l7_2 : forall M A B, is_midpoint M A B -> is_midpoint M B A.