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: lexicographic combination of reduction pairs: 1. matrix interpretations: carrier: N^3 order: lexicographic order interpretations: g#_A(x1) = ((1,0,0),(0,0,0),(1,1,0)) x1 c_A(x1,x2) = ((1,0,0),(0,0,0),(0,1,0)) x1 + ((1,0,0),(0,1,0),(1,0,1)) x2 + (0,1,0) s_A(x1) = ((1,0,0),(0,1,0),(0,1,1)) x1 + (1,1,0) 2. lexicographic path order with precedence: precedence: s > g# > c argument filter: pi(g#) = [] pi(c) = 2 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 monotone reduction pair: lexicographic combination of reduction pairs: 1. matrix interpretations: carrier: N^3 order: lexicographic order interpretations: f#_A(x1) = ((1,0,0),(1,1,0),(1,1,1)) x1 c_A(x1,x2) = ((1,0,0),(1,1,0),(1,1,1)) x1 + ((1,0,0),(0,1,0),(1,1,1)) x2 s_A(x1) = ((1,0,0),(0,1,0),(1,1,1)) x1 + (1,1,1) 2. lexicographic path order with precedence: precedence: f# > c > s argument filter: pi(f#) = 1 pi(c) = [1, 2] pi(s) = [1] The next rules are strictly ordered: p1 r1, r2, r3, r4 We remove them from the problem. Then no dependency pair remains.