YES We show the termination of the TRS R: f(g(x)) -> g(f(f(x))) f(h(x)) -> h(g(x)) |f'|(s(x),y,y) -> |f'|(y,x,s(x)) -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: f#(g(x)) -> f#(f(x)) p2: f#(g(x)) -> f#(x) p3: |f'|#(s(x),y,y) -> |f'|#(y,x,s(x)) and R consists of: r1: f(g(x)) -> g(f(f(x))) r2: f(h(x)) -> h(g(x)) r3: |f'|(s(x),y,y) -> |f'|(y,x,s(x)) The estimated dependency graph contains the following SCCs: {p1, p2} {p3} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: f#(g(x)) -> f#(f(x)) p2: f#(g(x)) -> f#(x) and R consists of: r1: f(g(x)) -> g(f(f(x))) r2: f(h(x)) -> h(g(x)) r3: |f'|(s(x),y,y) -> |f'|(y,x,s(x)) The set of usable rules consists of r1, r2 Take the reduction pair: lexicographic combination of reduction pairs: 1. matrix interpretations: carrier: N^4 order: lexicographic order interpretations: f#_A(x1) = ((0,0,0,0),(0,0,0,0),(1,0,0,0),(0,1,0,0)) x1 g_A(x1) = ((1,0,0,0),(1,1,0,0),(0,0,1,0),(0,1,0,0)) x1 + (0,1,1,0) f_A(x1) = ((1,0,0,0),(0,1,0,0),(0,1,0,0),(0,1,0,0)) x1 + (0,0,1,0) h_A(x1) = ((0,0,0,0),(1,0,0,0),(1,0,0,0),(0,0,0,0)) x1 + (1,1,1,0) 2. lexicographic path order with precedence: precedence: f > g > h > f# argument filter: pi(f#) = [] pi(g) = [] pi(f) = [] pi(h) = [] The next rules are strictly ordered: p1, p2 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'|#(s(x),y,y) -> |f'|#(y,x,s(x)) and R consists of: r1: f(g(x)) -> g(f(f(x))) r2: f(h(x)) -> h(g(x)) r3: |f'|(s(x),y,y) -> |f'|(y,x,s(x)) The set of usable rules consists of (no rules) Take the reduction pair: lexicographic combination of reduction pairs: 1. matrix interpretations: carrier: N^4 order: lexicographic order interpretations: |f'|#_A(x1,x2,x3) = ((1,0,0,0),(1,0,0,0),(1,1,0,0),(1,1,1,0)) x1 + ((0,0,0,0),(0,0,0,0),(1,0,0,0),(0,0,0,0)) x2 + ((1,0,0,0),(1,0,0,0),(0,1,0,0),(1,1,1,0)) x3 s_A(x1) = ((1,0,0,0),(1,0,0,0),(1,1,0,0),(1,1,1,0)) x1 + (1,1,1,1) 2. lexicographic path order with precedence: precedence: |f'|# > s argument filter: pi(|f'|#) = [] pi(s) = [] The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains.