Hint Resolve thm4_1c thm4_1d.

Theorem thm5_6 :
forall (l m n : Line) (H1 : ConLn l m) (H2 : EqLn m n),
EqPt (pt (Twol l m H1)) (pt (Twol l n (cong_eqln_con l m n H1 H2))).