proposition: Lemma lift_is_additive : additive (fglift f).
proof: Proof. elim/quotW=> [[D1 /= H1]]; elim/quotW=> [[D2 /= H2]]. unlock fglift; rewrite ?piE [_ + _]piE /lift /=. rewrite !prelift_repr /fgadd_r /fgopp_r /=. by rewrite !(prelift_reduce, prelift_cat, prelift_opp). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)