fact: Definition act_f (sc : col_squares) (p : {perm square}) : col_squares := [ffun z => sc (p^-1 z)].
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype tuple finfun bigop finset fingroup) mathcomp(action perm primitive_action)