proposition: Lemma porbitPb x y : y \in porbit s x -> exists i, y == (s ^+ i)%g x.
proof: Proof. Proof using. move=> /porbitP H. by move: H => [i Hi]; exists i; rewrite Hi. Qed.
imports: mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq choice fintype) mathcomp(tuple finfun finset path bigop) mathcomp(fingroup perm action) mathcomp(ssralg matrix mxalgebra algC classfun) partition tools sorted permcomp fibered_set cycles