fact: Variable (acts : Vector.t (option sig * move) n).
imports: Undecidability.TM.Basic.Mono Undecidability.TM.Combinators.Combinators Undecidability.TM.Code.Code Undecidability.TM.Single.EncodeTapes Undecidability.TM.Compound(TMTac MoveToSymbol Multi Shift)