Require Export GeoCoq.Tarski_dev.Ch12_parallel.
Require Export GeoCoq.Tarski_dev.Annexes.perp_bisect.
Section Triangles.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
Section ABC.
Variable A B C : Tpoint.
Definition isosceles A B C :=
Cong A B B C.

Lemma isosceles_sym :
isosceles A B C ->
isosceles C B A.