Input TRS:
    1: active(f(X)) -> mark(if(X,c(),f(true())))
    2: active(if(true(),X,Y)) -> mark(X)
    3: active(if(false(),X,Y)) -> mark(Y)
    4: active(f(X)) -> f(active(X))
    5: active(if(X1,X2,X3)) -> if(active(X1),X2,X3)
    6: active(if(X1,X2,X3)) -> if(X1,active(X2),X3)
    7: f(mark(X)) -> mark(f(X))
    8: if(mark(X1),X2,X3) -> mark(if(X1,X2,X3))
    9: if(X1,mark(X2),X3) -> mark(if(X1,X2,X3))
    10: proper(f(X)) -> f(proper(X))
    11: proper(if(X1,X2,X3)) -> if(proper(X1),proper(X2),proper(X3))
    12: proper(c()) -> ok(c())
    13: proper(true()) -> ok(true())
    14: proper(false()) -> ok(false())
    15: f(ok(X)) -> ok(f(X))
    16: if(ok(X1),ok(X2),ok(X3)) -> ok(if(X1,X2,X3))
    17: top(mark(X)) -> top(proper(X))
    18: top(ok(X)) -> top(active(X))
Number of Rules: 18
Direct POLO(mSum) ... failed.