Problem: h(x,y) -> f(x,y,x) f(0(),1(),x) -> h(x,x) g(x,y) -> x g(x,y) -> y Proof: Unfolding Processor: loop length: 4 terms: h(g(0(),1()),1()) f(g(0(),1()),1(),g(0(),1())) f(0(),1(),g(0(),1())) h(g(0(),1()),g(0(),1())) context: [] substitution: Qed