(STRATEGY
    INNERMOST)

(VAR
    X X1 X2 XS)
(DATATYPES
    A = µX.< zeros, mark(X), 0, ok(X) >)
(SIGNATURES
    active :: [A] -> A
    cons :: [A x A] -> A
    tail :: [A] -> A
    proper :: [A] -> A
    top :: [A] -> A)
(RULES
    active(zeros()) -> mark(cons(0()
                                ,zeros()))
    active(tail(cons(X,XS))) ->
      mark(XS)
    active(cons(X1,X2)) ->
      cons(active(X1),X2)
    active(tail(X)) ->
      tail(active(X))
    cons(mark(X1),X2) ->
      mark(cons(X1,X2))
    tail(mark(X)) -> mark(tail(X))
    proper(zeros()) -> ok(zeros())
    proper(cons(X1,X2)) ->
      cons(proper(X1),proper(X2))
    proper(0()) -> ok(0())
    proper(tail(X)) ->
      tail(proper(X))
    cons(ok(X1),ok(X2)) ->
      ok(cons(X1,X2))
    tail(ok(X)) -> ok(tail(X))
    top(mark(X)) -> top(proper(X))
    top(ok(X)) -> top(active(X)))