YES # Compositional parallel rule labeling (Shintani and Hirokawa 2022). Consider the left-linear TRS R: foo(0(x)) -> 0(s(p(p(p(s(s(s(p(s(x)))))))))) foo(s(x)) -> p(s(p(p(p(s(s(p(s(s(p(s(foo(p(p(s(s(p(s(bar(p(p(s(s(p(s(x)))))))))))))))))))))))))) bar(0(x)) -> 0(p(s(s(s(x))))) bar(s(x)) -> p(s(p(p(s(s(foo(s(p(p(s(s(x)))))))))))) p(p(s(x))) -> p(x) p(s(x)) -> x p(0(x)) -> 0(s(s(s(s(x))))) Let C be the following subset of R: (empty) All parallel critical peaks (except C's) are decreasing wrt rule labeling: phi(foo(0(x)) -> 0(s(p(p(p(s(s(s(p(s(x))))))))))) = 1 phi(foo(s(x)) -> p(s(p(p(p(s(s(p(s(s(p(s(foo(p(p(s(s(p(s(bar(p(p(s(s(p(s(x))))))))))))))))))))))))))) = 1 phi(bar(0(x)) -> 0(p(s(s(s(x)))))) = 1 phi(bar(s(x)) -> p(s(p(p(s(s(foo(s(p(p(s(s(x))))))))))))) = 1 phi(p(p(s(x))) -> p(x)) = 1 phi(p(s(x)) -> x) = 1 phi(p(0(x)) -> 0(s(s(s(s(x)))))) = 1 psi(foo(0(x)) -> 0(s(p(p(p(s(s(s(p(s(x))))))))))) = 1 psi(foo(s(x)) -> p(s(p(p(p(s(s(p(s(s(p(s(foo(p(p(s(s(p(s(bar(p(p(s(s(p(s(x))))))))))))))))))))))))))) = 1 psi(bar(0(x)) -> 0(p(s(s(s(x)))))) = 1 psi(bar(s(x)) -> p(s(p(p(s(s(foo(s(p(p(s(s(x))))))))))))) = 1 psi(p(p(s(x))) -> p(x)) = 1 psi(p(s(x)) -> x) = 1 psi(p(0(x)) -> 0(s(s(s(s(x)))))) = 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: (empty) Let C be the following subset of R: (empty) The parallel critical pair system PCPS(R,C) is: (empty) 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.