(STRATEGY
    INNERMOST)

(VAR
    I P X X1 X2 Y Z)
(DATATYPES
    A = µX.< mark(X), nil, tt, ok(X) >)
(SIGNATURES
    active :: [A] -> A
    __ :: [A x A] -> A
    and :: [A x A] -> A
    isNePal :: [A] -> A
    proper :: [A] -> A
    top :: [A] -> A)
(RULES
    active(__(__(X,Y),Z)) ->
      mark(__(X,__(Y,Z)))
    active(__(X,nil())) -> mark(X)
    active(__(nil(),X)) -> mark(X)
    active(and(tt(),X)) -> mark(X)
    active(isNePal(__(I
                     ,__(P,I)))) -> mark(tt())
    active(__(X1,X2)) ->
      __(active(X1),X2)
    active(__(X1,X2)) -> __(X1
                           ,active(X2))
    active(and(X1,X2)) ->
      and(active(X1),X2)
    active(isNePal(X)) ->
      isNePal(active(X))
    __(mark(X1),X2) -> mark(__(X1
                              ,X2))
    __(X1,mark(X2)) -> mark(__(X1
                              ,X2))
    and(mark(X1),X2) -> mark(and(X1
                                ,X2))
    isNePal(mark(X)) ->
      mark(isNePal(X))
    proper(__(X1,X2)) ->
      __(proper(X1),proper(X2))
    proper(nil()) -> ok(nil())
    proper(and(X1,X2)) ->
      and(proper(X1),proper(X2))
    proper(tt()) -> ok(tt())
    proper(isNePal(X)) ->
      isNePal(proper(X))
    __(ok(X1),ok(X2)) -> ok(__(X1
                              ,X2))
    and(ok(X1),ok(X2)) -> ok(and(X1
                                ,X2))
    isNePal(ok(X)) -> ok(isNePal(X))
    top(mark(X)) -> top(proper(X))
    top(ok(X)) -> top(active(X)))