fact: Fixpoint prelift_aux (n: nat) (P: Preterm) (k: nat) : Preterm := match P with | Fun _ => P | Var i => match (le_gt_dec k i) with | left _ => Var (i + n) | right _ => Var i end | App M N => App (prelift_aux n M k) (prelift_aux n N k) | Abs A M => Abs A (prelift_aux n M (S k)) end.
imports: Coq(Compare_dec Arith Lia) CoLoR(RelExtras ListExtras LogicUtil)