YES We show the termination of the TRS R: p(a(x0),p(b(x1),p(a(x2),x3))) -> p(x2,p(a(a(x0)),p(b(x1),x3))) -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: p#(a(x0),p(b(x1),p(a(x2),x3))) -> p#(x2,p(a(a(x0)),p(b(x1),x3))) p2: p#(a(x0),p(b(x1),p(a(x2),x3))) -> p#(a(a(x0)),p(b(x1),x3)) p3: p#(a(x0),p(b(x1),p(a(x2),x3))) -> p#(b(x1),x3) and R consists of: r1: p(a(x0),p(b(x1),p(a(x2),x3))) -> p(x2,p(a(a(x0)),p(b(x1),x3))) The estimated dependency graph contains the following SCCs: {p2} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: p#(a(x0),p(b(x1),p(a(x2),x3))) -> p#(a(a(x0)),p(b(x1),x3)) and R consists of: r1: p(a(x0),p(b(x1),p(a(x2),x3))) -> p(x2,p(a(a(x0)),p(b(x1),x3))) 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: b > a > p# > p argument filter: pi(p#) = [1, 2] pi(a) = 1 pi(p) = [1, 2] pi(b) = 1 2. lexicographic path order with precedence: precedence: a > p# > b > p argument filter: pi(p#) = [1] pi(a) = 1 pi(p) = [1, 2] pi(b) = [1] 3. lexicographic path order with precedence: precedence: a > p > b > p# argument filter: pi(p#) = 1 pi(a) = [] pi(p) = [1, 2] pi(b) = 1 The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains.