fact: Definition up_i `{funcs_signature} (σi : nat -> term) := econs (var_indi 0) (fun x => (σi x)[shift]i).
imports: Arith Lia Vector Undecidability.Shared.Libs.PSL(Vectors) Undecidability.SOL.Util(Syntax) Undecidability.SOL.SOL