YES # Compositional parallel rule labeling (Shintani and Hirokawa 2022). Consider the left-linear TRS R: +(x,0()) -> x +(x,s(y)) -> s(+(x,y)) +(x,p(y)) -> p(+(x,y)) +(0(),y) -> y +(s(x),y) -> s(+(x,y)) +(p(x),y) -> p(+(x,y)) s(p(x)) -> x p(s(x)) -> x +(+(x,y),z) -> +(x,+(y,z)) +(x,+(y,z)) -> +(+(x,y),z) Let C be the following subset of R: +(x,s(y)) -> s(+(x,y)) +(x,p(y)) -> p(+(x,y)) +(0(),y) -> y +(s(x),y) -> s(+(x,y)) +(p(x),y) -> p(+(x,y)) s(p(x)) -> x p(s(x)) -> x +(+(x,y),z) -> +(x,+(y,z)) All parallel critical peaks (except C's) are decreasing wrt rule labeling: phi(+(x,0()) -> x) = 1 phi(+(x,s(y)) -> s(+(x,y))) = 0 phi(+(x,p(y)) -> p(+(x,y))) = 0 phi(+(0(),y) -> y) = 0 phi(+(s(x),y) -> s(+(x,y))) = 0 phi(+(p(x),y) -> p(+(x,y))) = 0 phi(s(p(x)) -> x) = 0 phi(p(s(x)) -> x) = 0 phi(+(+(x,y),z) -> +(x,+(y,z))) = 0 phi(+(x,+(y,z)) -> +(+(x,y),z)) = 1 psi(+(x,0()) -> x) = 1 psi(+(x,s(y)) -> s(+(x,y))) = 0 psi(+(x,p(y)) -> p(+(x,y))) = 0 psi(+(0(),y) -> y) = 0 psi(+(s(x),y) -> s(+(x,y))) = 0 psi(+(p(x),y) -> p(+(x,y))) = 0 psi(s(p(x)) -> x) = 0 psi(p(s(x)) -> x) = 0 psi(+(+(x,y),z) -> +(x,+(y,z))) = 0 psi(+(x,+(y,z)) -> +(+(x,y),z)) = 1 Therefore, the confluence of R follows from that of C. # Compositional parallel critical pair system (Shintani and Hirokawa 2022). Consider the left-linear TRS R: +(x,s(y)) -> s(+(x,y)) +(x,p(y)) -> p(+(x,y)) +(0(),y) -> y +(s(x),y) -> s(+(x,y)) +(p(x),y) -> p(+(x,y)) s(p(x)) -> x p(s(x)) -> x +(+(x,y),z) -> +(x,+(y,z)) Let C be the following subset of R: (empty) The parallel critical pair system PCPS(R,C) is: +(0(),s(y2)) -> s(y2) +(0(),s(y2)) -> s(+(0(),y2)) +(s(x0_1),s(y2)) -> s(+(x0_1,s(y2))) +(s(x0_1),s(y2)) -> s(+(s(x0_1),y2)) +(p(x0_1),s(y2)) -> p(+(x0_1,s(y2))) +(p(x0_1),s(y2)) -> s(+(p(x0_1),y2)) +(+(x0_1,x0_2),s(y2)) -> +(x0_1,+(x0_2,s(y2))) +(+(x0_1,x0_2),s(y2)) -> s(+(+(x0_1,x0_2),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)) +(s(x0_1),p(y2)) -> s(+(x0_1,p(y2))) +(s(x0_1),p(y2)) -> p(+(s(x0_1),y2)) +(p(x0_1),p(y2)) -> p(+(x0_1,p(y2))) +(p(x0_1),p(y2)) -> p(+(p(x0_1),y2)) +(+(x0_1,x0_2),p(y2)) -> +(x0_1,+(x0_2,p(y2))) +(+(x0_1,x0_2),p(y2)) -> p(+(+(x0_1,x0_2),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) +(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)) +(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)) +(+(y1,y2),s(x0_2)) -> s(+(+(y1,y2),x0_2)) +(+(y1,y2),s(x0_2)) -> +(y1,+(y2,s(x0_2))) +(+(y1,y2),p(x0_2)) -> p(+(+(y1,y2),x0_2)) +(+(y1,y2),p(x0_2)) -> +(y1,+(y2,p(x0_2))) +(+(y1,s(x1_2)),y3) -> +(s(+(y1,x1_2)),y3) +(+(y1,s(x1_2)),y3) -> +(y1,+(s(x1_2),y3)) +(+(y1,p(x1_2)),y3) -> +(p(+(y1,x1_2)),y3) +(+(y1,p(x1_2)),y3) -> +(y1,+(p(x1_2),y3)) +(+(0(),y2),y3) -> +(y2,y3) +(+(0(),y2),y3) -> +(0(),+(y2,y3)) +(+(s(x1_1),y2),y3) -> +(s(+(x1_1,y2)),y3) +(+(s(x1_1),y2),y3) -> +(s(x1_1),+(y2,y3)) +(+(p(x1_1),y2),y3) -> +(p(+(x1_1,y2)),y3) +(+(p(x1_1),y2),y3) -> +(p(x1_1),+(y2,y3)) +(+(+(x1_1,x1_2),y2),y3) -> +(+(x1_1,+(x1_2,y2)),y3) +(+(+(x1_1,x1_2),y2),y3) -> +(+(x1_1,x1_2),+(y2,y3)) 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.