fact: Fixpoint bnats (n: nat): @sig2 (list nat) (below_in n) no_dups.
imports: Coq(FunctionalExtensionality Arith Lia) Coq(Arith.Peano_dec Arith.Compare_dec) Coq(Relations.Relation_Operators) Coq(List) Chapar(Predefs)