fact: Definition natsum_of_int (m : int) : nat + nat := match m with Posz p => inl _ p | Negz n => inr _ n end.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)