Section TarskiGe1.
Variable R : realFieldType.
Variable n : nat.
Implicit Types (a b c d : (@ Vector R n)).
Definition cong a b c d := (b - a) *m (b - a)^T == (d - c) *m (d - c)^T.

Lemma betS_sym a b c : betS a b c = betS c b a.
Definition bet a b c := betE a b c || betS a b c.