(* Gabriel Braun February 2013 *)
Require Export GeoCoq.Tarski_dev.Annexes.quadrilaterals_inter_dec.
Section Vectors.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.

Lemma opposite_sum :
forall A B C D E F,
SumV A B C D E F ->
SumV B A D C F E.