YES ---- CR(R) ---- [Jouannaud and Kirchner, 1986] R: +(+(x,y),z) -> +(x,+(y,z)) +(x,y) -> +(y,x) *(+(x,y),z) -> +(*(x,z),*(y,z)) *(x,+(y,z)) -> +(*(x,y),*(x,z)) CP_AC(R): +(*(x,+(y,z)),*(w,+(y,z))) -> +(*(+(x,w),y),*(+(x,w),z)) +(*(+(x,y),z),*(+(x,y),w)) -> +(*(x,+(z,w)),*(y,+(z,w)))