proposition: Lemma BQsum_le2l a b c: ratp a -> ratp b -> ratp c -> ((c +q a) <=q (c +q b) <-> a <=q b).
proof: Proof. move => pa pb pc. apply: (iff_trans (qle_diffP (QSs pc pa) (QSs pc pb))). apply: iff_sym;apply: (iff_trans (qle_diffP pa pb)). by rewrite BQdiff_sum_simpl_l. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)