proposition: Lemma fgaddgN : right_inverse fgzero fgopp fgadd.
proof: Proof. by move=> x; rewrite fgaddC fgaddNg. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap