YES We show the termination of the TRS R: f(c(s(x),y)) -> f(c(x,s(y))) f(c(s(x),s(y))) -> g(c(x,y)) g(c(x,s(y))) -> g(c(s(x),y)) g(c(s(x),s(y))) -> f(c(x,y)) -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: f#(c(s(x),y)) -> f#(c(x,s(y))) p2: f#(c(s(x),s(y))) -> g#(c(x,y)) p3: g#(c(x,s(y))) -> g#(c(s(x),y)) p4: g#(c(s(x),s(y))) -> f#(c(x,y)) and R consists of: r1: f(c(s(x),y)) -> f(c(x,s(y))) r2: f(c(s(x),s(y))) -> g(c(x,y)) r3: g(c(x,s(y))) -> g(c(s(x),y)) r4: g(c(s(x),s(y))) -> f(c(x,y)) The estimated dependency graph contains the following SCCs: {p1, p2, p3, p4} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: f#(c(s(x),y)) -> f#(c(x,s(y))) p2: f#(c(s(x),s(y))) -> g#(c(x,y)) p3: g#(c(s(x),s(y))) -> f#(c(x,y)) p4: g#(c(x,s(y))) -> g#(c(s(x),y)) and R consists of: r1: f(c(s(x),y)) -> f(c(x,s(y))) r2: f(c(s(x),s(y))) -> g(c(x,y)) r3: g(c(x,s(y))) -> g(c(s(x),y)) r4: g(c(s(x),s(y))) -> f(c(x,y)) The set of usable rules consists of (no rules) Take the reduction pair: lexicographic combination of reduction pairs: 1. lexicographic path order with precedence: precedence: f# > g# > c > s argument filter: pi(f#) = 1 pi(c) = [1, 2] pi(s) = 1 pi(g#) = 1 2. matrix interpretations: carrier: N^3 order: lexicographic order interpretations: f#_A(x1) = ((1,0,0),(0,1,0),(1,0,1)) x1 + (0,0,1) c_A(x1,x2) = ((0,0,0),(1,0,0),(1,1,0)) x1 + ((1,0,0),(0,0,0),(0,1,0)) x2 + (0,1,1) s_A(x1) = x1 + (0,1,1) g#_A(x1) = ((1,0,0),(0,1,0),(1,0,1)) x1 The next rules are strictly ordered: p2, p3 We remove them from the problem. -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: f#(c(s(x),y)) -> f#(c(x,s(y))) p2: g#(c(x,s(y))) -> g#(c(s(x),y)) and R consists of: r1: f(c(s(x),y)) -> f(c(x,s(y))) r2: f(c(s(x),s(y))) -> g(c(x,y)) r3: g(c(x,s(y))) -> g(c(s(x),y)) r4: g(c(s(x),s(y))) -> f(c(x,y)) The estimated dependency graph contains the following SCCs: {p1} {p2} -- 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: f(c(s(x),y)) -> f(c(x,s(y))) r2: f(c(s(x),s(y))) -> g(c(x,y)) r3: g(c(x,s(y))) -> g(c(s(x),y)) r4: g(c(s(x),s(y))) -> f(c(x,y)) The set of usable rules consists of (no rules) Take the reduction pair: lexicographic combination of reduction pairs: 1. lexicographic path order with precedence: precedence: c > s > f# argument filter: pi(f#) = [1] pi(c) = [1, 2] pi(s) = [1] 2. matrix interpretations: carrier: N^3 order: lexicographic order interpretations: f#_A(x1) = ((1,0,0),(1,1,0),(1,0,1)) x1 c_A(x1,x2) = ((1,0,0),(0,0,0),(1,1,0)) x1 + x2 + (0,1,0) s_A(x1) = ((1,0,0),(0,1,0),(1,1,1)) x1 + (1,1,3) 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: g#(c(x,s(y))) -> g#(c(s(x),y)) and R consists of: r1: f(c(s(x),y)) -> f(c(x,s(y))) r2: f(c(s(x),s(y))) -> g(c(x,y)) r3: g(c(x,s(y))) -> g(c(s(x),y)) r4: g(c(s(x),s(y))) -> f(c(x,y)) The set of usable rules consists of (no rules) Take the reduction pair: lexicographic combination of reduction pairs: 1. lexicographic path order with precedence: precedence: g# > s > c argument filter: pi(g#) = [1] pi(c) = [1, 2] pi(s) = 1 2. matrix interpretations: carrier: N^3 order: lexicographic order interpretations: g#_A(x1) = ((1,0,0),(0,1,0),(1,1,1)) x1 c_A(x1,x2) = ((0,0,0),(1,0,0),(0,0,0)) x1 + ((1,0,0),(1,1,0),(1,1,1)) x2 + (1,0,1) s_A(x1) = ((1,0,0),(0,1,0),(1,0,1)) x1 + (1,1,1) The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains.