fact: Definition cast_set n m (H : n = m) : {set 'I_n} -> {set 'I_m} := [fun s : {set 'I_n} => (cast_ord H) @: s].
imports: mathcomp.ssreflect.ssreflect mathcomp(ssreflect ssrbool ssrfun ssrnat eqtype finfun fintype choice seq tuple) mathcomp(finset tuple bigop) tools