YES Problem: +(x,0()) -> x +(s(x),y) -> s(+(x,y)) +(x,y) -> +(y,x) Proof: AT confluence processor Complete TRS T' of input TRS: +(x,0()) -> x +(s(x),y) -> s(+(x,y)) +(0(),y) -> y +(x,s(x20)) -> s(+(x,x20)) +(x,y) -> +(y,x) T' = (P union S) with TRS P:+(x,y) -> +(y,x) TRS S:+(x,0()) -> x +(s(x),y) -> s(+(x,y)) +(0(),y) -> y +(x,s(x20)) -> s(+(x,x20)) S is left-linear and P is reversible. CP(S,S) = s(x) = s(+(x,0())), 0() = 0(), s(+(x172,0())) = s(x172), s(+(x174,s(x20))) = s(+(s(x174),x20)), s(x20) = s(+(0(),x20)), s(+(s(x),x179)) = s(+(x,s(x179))), s(+(0(),x181)) = s(x181) CP(S,P union P^-1) = x = +(0(),x), y = +(0(),y), s(+(x196,y)) = +(y,s(x196)), s(+(x198,x)) = +(x,s(x198)), y = +(y,0()), x = +(x,0()), s(+(x,x203)) = +(s(x203),x), s(+(y,x205)) = +(s(x205),y) PCP_in(P union P^-1,S) = We have to check termination of S: Matrix Interpretation Processor: dim=1 interpretation: [+](x0, x1) = x0 + 2x1 + 7, [0] = 6, [s](x0) = x0 orientation: +(x,0()) = x + 19 >= x = x +(s(x),y) = x + 2y + 7 >= x + 2y + 7 = s(+(x,y)) +(0(),y) = 2y + 13 >= y = y +(x,s(x20)) = x + 2x20 + 7 >= x + 2x20 + 7 = s(+(x,x20)) problem: +(s(x),y) -> s(+(x,y)) +(x,s(x20)) -> s(+(x,x20)) Matrix Interpretation Processor: dim=1 interpretation: [+](x0, x1) = x0 + 2x1 + 7, [s](x0) = x0 + 6 orientation: +(s(x),y) = x + 2y + 13 >= x + 2y + 13 = s(+(x,y)) +(x,s(x20)) = x + 2x20 + 19 >= x + 2x20 + 13 = s(+(x,x20)) problem: +(s(x),y) -> s(+(x,y)) Matrix Interpretation Processor: dim=1 interpretation: [+](x0, x1) = 6x0 + x1 + 2, [s](x0) = x0 + 3 orientation: +(s(x),y) = 6x + y + 20 >= 6x + y + 5 = s(+(x,y)) problem: Qed