fact: Definition flatten_partition {X n} (f:stn n -> nat) (x:stn (stnsum f) -> X) : flatten (partition f x) ~ x.
imports: UniMath.Combinatorics.FiniteSets UniMath.Combinatorics.Lists UniMath.Combinatorics.Vectors UniMath.MoreFoundations.PartA UniMath.MoreFoundations.Tactics