fact: Record INV l1 l2 acc : Prop := { l1_sorted : sort X.lt (rev l1); l2_sorted : sort X.lt (rev l2); acc_sorted : sort X.lt acc; l1_lt_acc x y : InA X.eq x l1 -> InA X.eq y acc -> X.lt x y; l2_lt_acc x y : InA X.eq x l2 -> InA X.eq y acc -> X.lt x y}.
imports: Bool List BinPos Pnat Setoid SetoidList PeanoNat