YES We show the termination of the TRS R: rev(nil()) -> nil() rev(cons(x,l)) -> cons(rev1(x,l),rev2(x,l)) rev1(|0|(),nil()) -> |0|() rev1(s(x),nil()) -> s(x) rev1(x,cons(y,l)) -> rev1(y,l) rev2(x,nil()) -> nil() rev2(x,cons(y,l)) -> rev(cons(x,rev2(y,l))) -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: rev#(cons(x,l)) -> rev1#(x,l) p2: rev#(cons(x,l)) -> rev2#(x,l) p3: rev1#(x,cons(y,l)) -> rev1#(y,l) p4: rev2#(x,cons(y,l)) -> rev#(cons(x,rev2(y,l))) p5: rev2#(x,cons(y,l)) -> rev2#(y,l) and R consists of: r1: rev(nil()) -> nil() r2: rev(cons(x,l)) -> cons(rev1(x,l),rev2(x,l)) r3: rev1(|0|(),nil()) -> |0|() r4: rev1(s(x),nil()) -> s(x) r5: rev1(x,cons(y,l)) -> rev1(y,l) r6: rev2(x,nil()) -> nil() r7: rev2(x,cons(y,l)) -> rev(cons(x,rev2(y,l))) The estimated dependency graph contains the following SCCs: {p2, p4, p5} {p3} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: rev2#(x,cons(y,l)) -> rev#(cons(x,rev2(y,l))) p2: rev#(cons(x,l)) -> rev2#(x,l) p3: rev2#(x,cons(y,l)) -> rev2#(y,l) and R consists of: r1: rev(nil()) -> nil() r2: rev(cons(x,l)) -> cons(rev1(x,l),rev2(x,l)) r3: rev1(|0|(),nil()) -> |0|() r4: rev1(s(x),nil()) -> s(x) r5: rev1(x,cons(y,l)) -> rev1(y,l) r6: rev2(x,nil()) -> nil() r7: rev2(x,cons(y,l)) -> rev(cons(x,rev2(y,l))) The set of usable rules consists of r2, r3, r4, r5, r6, r7 Take the reduction pair: max/plus interpretations on natural numbers: rev2#_A(x1,x2) = max{1, x2 - 2} cons_A(x1,x2) = x2 + 5 rev#_A(x1) = max{0, x1 - 2} rev2_A(x1,x2) = x2 rev1_A(x1,x2) = max{1, x2 - 6} |0|_A = 0 nil_A = 6 s_A(x1) = 1 rev_A(x1) = max{3, 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: rev2#(x,cons(y,l)) -> rev#(cons(x,rev2(y,l))) and R consists of: r1: rev(nil()) -> nil() r2: rev(cons(x,l)) -> cons(rev1(x,l),rev2(x,l)) r3: rev1(|0|(),nil()) -> |0|() r4: rev1(s(x),nil()) -> s(x) r5: rev1(x,cons(y,l)) -> rev1(y,l) r6: rev2(x,nil()) -> nil() r7: rev2(x,cons(y,l)) -> rev(cons(x,rev2(y,l))) The estimated dependency graph contains the following SCCs: (no SCCs) -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: rev1#(x,cons(y,l)) -> rev1#(y,l) and R consists of: r1: rev(nil()) -> nil() r2: rev(cons(x,l)) -> cons(rev1(x,l),rev2(x,l)) r3: rev1(|0|(),nil()) -> |0|() r4: rev1(s(x),nil()) -> s(x) r5: rev1(x,cons(y,l)) -> rev1(y,l) r6: rev2(x,nil()) -> nil() r7: rev2(x,cons(y,l)) -> rev(cons(x,rev2(y,l))) The set of usable rules consists of (no rules) Take the reduction pair: max/plus interpretations on natural numbers: rev1#_A(x1,x2) = max{x1 + 1, x2} cons_A(x1,x2) = max{x1 + 2, x2 + 1} The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains.