YES (ignored inputs)COMMENT from the collection of \cite{AT2012} Rewrite Rules: [ max(?x,0) -> ?x, max(0,?y) -> ?y, max(s(?x),s(?y)) -> s(max(?x,?y)), max(?x,?y) -> max(?y,?x) ] Apply Direct Methods... Inner CPs: [ ] Outer CPs: [ 0 = 0, ?x = max(0,?x), ?y_1 = max(?y_1,0), s(max(?x_2,?y_2)) = max(s(?y_2),s(?x_2)) ] Overlay, check Innermost Termination... unknown Innermost Terminating unknown Knuth & Bendix Linear Development Closed Direct Methods: CR Final result: CR 205.trs: Success(CR) (0 msec.)