proposition: Fact add0fx : left_id subfext0 subfext_add.
proof: Proof. by move=> x; rewrite -[x]reprK !piE add0r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype tuple finfun bigop ssralg countalg) mathcomp(finalg zmodp matrix vector falgebra poly polydiv) mathcomp(mxpoly generic_quotient)