YES Problem: +(x,y) -> +(y,x) +(0(),y) -> y +(x,0()) -> x +(s(x),y) -> s(+(x,y)) +(x,+(y,z)) -> +(+(x,y),z) Proof: AT confluence processor Complete TRS T' of input TRS: +(0(),y) -> y +(x,0()) -> x +(s(x),y) -> s(+(x,y)) +(y,s(x)) -> s(+(y,x)) +(x,y) -> +(y,x) +(x,+(y,z)) -> +(+(x,y),z) T' = (P union S) with TRS P:+(x,y) -> +(y,x) +(x,+(y,z)) -> +(+(x,y),z) TRS S:+(0(),y) -> y +(x,0()) -> x +(s(x),y) -> s(+(x,y)) +(y,s(x)) -> s(+(y,x)) S is linear and P is reversible. CP(S,S) = 0() = 0(), s(x) = s(+(0(),x)), s(x) = s(+(x,0())), s(+(x370,0())) = s(x370), s(+(x372,s(x))) = s(+(s(x372),x)), s(+(0(),x375)) = s(x375), s(+(s(x),x377)) = s(+(x,s(x377))) CP(S,P union P^-1) = y = +(y,0()), +(y,z) = +(+(0(),y),z), +(x,z) = +(+(x,0()),z), x = +(x,0()), +(y,z) = +(0(),+(y,z)), x = +(0(),x), +(x,y) = +(+(x,y),0()), y = +(0(),y), +(x,y) = +(x,+(y,0())), +(x,z) = +(x,+(0(),z)), s(+(x424,y)) = +(y,s(x424)), s(+(x426,+(y,z))) = +(+(s(x426),y),z), +(x,s(+(x428,z))) = +(+(x,s(x428)),z), s(+(x430,x)) = +(x,s(x430)), +(s(+(x432,y)),z) = +(s(x432),+(y,z)), s(+(x,x435)) = +(s(x435),x), +(x,s(+(y,x437))) = +(+(x,y),s(x437)), s(+(y,x439)) = +(s(x439),y), s(+(+(x,y),x441)) = +(x,+(y,s(x441))), +(s(+(x,x443)),z) = +(x,+(s(x443),z)) CP(P union P^-1,S) = +(y,0()) = y, +(0(),x) = x, +(y,s(x)) = s(+(x,y)), +(s(x),y) = s(+(y,x)), +(+(0(),x533),x534) = +(x533,x534), +(+(s(x),x536),x537) = s(+(x,+(x536,x537))), +(x546,+(x547,0())) = +(x546,x547), +(x549,+(x550,s(x))) = s(+(+(x549,x550),x)) We have to check termination of S: Matrix Interpretation Processor: dim=1 interpretation: [0] = 2, [+](x0, x1) = 2x0 + x1 + 2, [s](x0) = x0 + 2 orientation: +(0(),y) = y + 6 >= y = y +(x,0()) = 2x + 4 >= x = x +(s(x),y) = 2x + y + 6 >= 2x + y + 4 = s(+(x,y)) +(y,s(x)) = x + 2y + 4 >= x + 2y + 4 = s(+(y,x)) problem: +(y,s(x)) -> s(+(y,x)) Matrix Interpretation Processor: dim=1 interpretation: [+](x0, x1) = x0 + 4x1 + 7, [s](x0) = x0 + 1 orientation: +(y,s(x)) = 4x + y + 11 >= 4x + y + 8 = s(+(y,x)) problem: Qed