+(* (∃rs'.rs = rs0@rs' ∧ current ? (nth j ? outt (niltape ?)) = None ?) ∨
+ (∃rs0'.rs0 = rs@rs0' ∧
+ outt = change_vec ??
+ (change_vec ?? int
+ (mk_tape sig (reverse sig rs@x::ls) (None sig) []) i)
+ (mk_tape sig (reverse sig rs@x::ls0) (option_hd sig rs0')
+ (tail sig rs0')) j) ∨
+ (∃xs,ci,cj,rs',rs0'.ci ≠ cj ∧ rs = xs@ci::rs' ∧ rs0 = xs@cj::rs0' ∧
+ outt = change_vec ??
+ (change_vec ?? int (midtape sig (reverse ? xs@x::ls) ci rs') i)
+ (midtape sig (reverse ? xs@x::ls0) cj rs0') j)).*)