fact: Definition split {m n} (i : 'I_(m + n)) : 'I_m + 'I_n := match ltnP (i) m with | LtnNotGeq lt_i_m => inl _ (Ordinal lt_i_m) | GeqNotLtn ge_i_m => inr _ (Ordinal (split_subproof ge_i_m)) end.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(path div)