NO Problem: strict: top(ok(U(x,y))) -> top(check(D(x,y))) D(x,B()) -> U(x,B()) F(x,U(O(y),z)) -> U(x,F(y,z)) F(x,U(N(y),z)) -> U(x,F(y,z)) D(O(x),F(y,z)) -> F(x,D(y,z)) D(N(x),F(y,z)) -> F(x,D(y,z)) F(x,U(E(),y)) -> U(x,F(E(),y)) D(E(),F(x,y)) -> F(E(),D(x,y)) weak: U(O(x),y) -> U(x,y) U(N(x),y) -> U(x,y) D(O(x),y) -> D(x,y) D(N(x),y) -> D(x,y) E() -> N(E()) check(O(x)) -> ok(O(x)) check(U(x,y)) -> U(check(x),y) check(U(x,y)) -> U(x,check(y)) check(D(x,y)) -> D(check(x),y) check(D(x,y)) -> D(x,check(y)) check(F(x,y)) -> F(check(x),y) check(F(x,y)) -> F(x,check(y)) check(O(x)) -> O(check(x)) check(N(x)) -> N(check(x)) U(ok(x),y) -> ok(U(x,y)) U(x,ok(y)) -> ok(U(x,y)) D(ok(x),y) -> ok(D(x,y)) D(x,ok(y)) -> ok(D(x,y)) F(ok(x),y) -> ok(F(x,y)) F(x,ok(y)) -> ok(F(x,y)) O(ok(x)) -> ok(O(x)) N(ok(x)) -> ok(N(x)) Proof: Unfolding Processor: loop length: 5 terms: top(ok(U(O(x426584),B()))) top(check(D(O(x426584),B()))) top(D(check(O(x426584)),B())) top(U(check(O(x426584)),B())) top(U(ok(O(x426584)),B())) context: [] substitution: x426584 -> x426584 Qed