Problem: *(X,+(Y,1())) -> +(*(X,+(Y,*(1(),0()))),X) *(X,1()) -> X *(X,0()) -> X *(X,0()) -> 0() Proof: Unfolding Processor: loop length: 2 terms: *(X,+(Y,1())) +(*(X,+(Y,*(1(),0()))),X) context: +([],X) substitution: X -> X Y -> Y Qed