fact: Fixpoint reduces (u v : seq 'I_n) := match u with | [::] | [:: _] => false | [:: a, b & l] => ((a == b) && (l == v)) || if v is v0 :: v' then (a == v0) && reduces (b :: l) v' else false end.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(fingroup perm morphism presentation) mathcomp(ssralg poly ssrint) permcomp tools permuted combclass congr