Ltac prolong A B x C D :=
 assert (sg:= Msegment_construction A B C D);
 ex_and sg x.

Lemma LmCoghGrab : forall A B C D E F, A <> B -> BetM B A C -> BetM D A E -> CongM B A D A -> CongM A C A E -> CongM B F D F -> CongM F C E F.