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.

(* Specifications: *)
Lemma isosceles_sym :
isosceles A B C ->
isosceles C B A.
Lemma isosceles_conga :
A<>C -> A<>B ->
isosceles A B C ->
CongA C A B A C B.
Lemma conga_isosceles :
~ Col A B C ->
CongA C A B A C B ->
isosceles A B C.