proposition: Lemma swapXYK : involutive swapXY.
proof: Proof. by move=> u; apply/polyP=> i; apply/polyP=> j; rewrite !coef_swapXY. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype choice ssrnat seq) mathcomp(fintype tuple finfun bigop fingroup perm div) mathcomp(ssralg zmodp matrix mxalgebra) mathcomp(poly polydiv mxpoly binomial)