proposition: Lemma qle_diffP1 a b: ratp a -> ratp b -> (a <=q b <-> \0q <=q (b -q a)).
proof: Proof. move => pa pb; apply: (iff_trans (qle_diffP pa pb)). symmetry; apply:qle0xP. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)