YES # Compositional parallel critical pair system (Shintani and Hirokawa 2022). Consider the left-linear TRS R: s(p(x)) -> x p(s(x)) -> x +(x,0()) -> x +(x,s(y)) -> s(+(x,y)) +(x,p(y)) -> p(+(x,y)) +(0(),y) -> y +(p(x),y) -> p(+(x,y)) +(s(x),y) -> s(+(x,y)) Let C be the following subset of R: (empty) The parallel critical pair system PCPS(R,C) is: +(p(x0_1),0()) -> p(+(x0_1,0())) +(p(x0_1),0()) -> p(x0_1) +(s(x0_1),0()) -> s(+(x0_1,0())) +(s(x0_1),0()) -> s(x0_1) +(0(),s(y2)) -> s(y2) +(0(),s(y2)) -> s(+(0(),y2)) +(p(x0_1),s(y2)) -> p(+(x0_1,s(y2))) +(p(x0_1),s(y2)) -> s(+(p(x0_1),y2)) +(s(x0_1),s(y2)) -> s(+(x0_1,s(y2))) +(s(x0_1),s(y2)) -> s(+(s(x0_1),y2)) +(y1,s(p(x1_1))) -> +(y1,x1_1) +(y1,s(p(x1_1))) -> s(+(y1,p(x1_1))) +(0(),p(y2)) -> p(y2) +(0(),p(y2)) -> p(+(0(),y2)) +(p(x0_1),p(y2)) -> p(+(x0_1,p(y2))) +(p(x0_1),p(y2)) -> p(+(p(x0_1),y2)) +(s(x0_1),p(y2)) -> s(+(x0_1,p(y2))) +(s(x0_1),p(y2)) -> p(+(s(x0_1),y2)) +(y1,p(s(x1_1))) -> +(y1,x1_1) +(y1,p(s(x1_1))) -> p(+(y1,s(x1_1))) +(0(),s(x0_2)) -> s(+(0(),x0_2)) +(0(),s(x0_2)) -> s(x0_2) +(0(),p(x0_2)) -> p(+(0(),x0_2)) +(0(),p(x0_2)) -> p(x0_2) +(p(y1),0()) -> p(y1) +(p(y1),0()) -> p(+(y1,0())) +(p(y1),s(x0_2)) -> s(+(p(y1),x0_2)) +(p(y1),s(x0_2)) -> p(+(y1,s(x0_2))) +(p(y1),p(x0_2)) -> p(+(p(y1),x0_2)) +(p(y1),p(x0_2)) -> p(+(y1,p(x0_2))) +(p(s(x1_1)),y2) -> +(x1_1,y2) +(p(s(x1_1)),y2) -> p(+(s(x1_1),y2)) +(s(y1),0()) -> s(y1) +(s(y1),0()) -> s(+(y1,0())) +(s(y1),s(x0_2)) -> s(+(s(y1),x0_2)) +(s(y1),s(x0_2)) -> s(+(y1,s(x0_2))) +(s(y1),p(x0_2)) -> p(+(s(y1),x0_2)) +(s(y1),p(x0_2)) -> s(+(y1,p(x0_2))) +(s(p(x1_1)),y2) -> +(x1_1,y2) +(s(p(x1_1)),y2) -> s(+(p(x1_1),y2)) All pairs in PCP(R) are joinable and PCPS(R,C)/R is terminating. Therefore, the confluence of R follows from that of C. # emptiness The empty TRS is confluent.