YES We show the termination of the TRS R: g(c(x,s(y))) -> g(c(s(x),y)) f(c(s(x),y)) -> f(c(x,s(y))) f(f(x)) -> f(d(f(x))) f(x) -> x -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: g#(c(x,s(y))) -> g#(c(s(x),y)) p2: f#(c(s(x),y)) -> f#(c(x,s(y))) p3: f#(f(x)) -> f#(d(f(x))) and R consists of: r1: g(c(x,s(y))) -> g(c(s(x),y)) r2: f(c(s(x),y)) -> f(c(x,s(y))) r3: f(f(x)) -> f(d(f(x))) r4: f(x) -> x The estimated dependency graph contains the following SCCs: {p1} {p2} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: g#(c(x,s(y))) -> g#(c(s(x),y)) and R consists of: r1: g(c(x,s(y))) -> g(c(s(x),y)) r2: f(c(s(x),y)) -> f(c(x,s(y))) r3: f(f(x)) -> f(d(f(x))) r4: f(x) -> x The set of usable rules consists of (no rules) Take the reduction pair: weighted path order base order: max/plus interpretations on natural numbers: g#_A(x1) = x1 c_A(x1,x2) = max{1, x2 - 2} s_A(x1) = max{4, x1 + 1} precedence: g# = c = s partial status: pi(g#) = [1] pi(c) = [] pi(s) = [1] The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains. -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: f#(c(s(x),y)) -> f#(c(x,s(y))) and R consists of: r1: g(c(x,s(y))) -> g(c(s(x),y)) r2: f(c(s(x),y)) -> f(c(x,s(y))) r3: f(f(x)) -> f(d(f(x))) r4: f(x) -> x The set of usable rules consists of (no rules) Take the reduction pair: weighted path order base order: max/plus interpretations on natural numbers: f#_A(x1) = x1 + 2 c_A(x1,x2) = max{0, x1 - 6} s_A(x1) = max{9, x1 + 3} precedence: f# = c = s partial status: pi(f#) = [1] pi(c) = [] pi(s) = [1] The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains.