YES We show the termination of the TRS R: cond1(true(),x) -> cond2(even(x),x) cond2(true(),x) -> cond1(neq(x,|0|()),div2(x)) cond2(false(),x) -> cond1(neq(x,|0|()),p(x)) neq(|0|(),|0|()) -> false() neq(|0|(),s(x)) -> true() neq(s(x),|0|()) -> true() neq(s(x),s(y())) -> neq(x,y()) even(|0|()) -> true() even(s(|0|())) -> false() even(s(s(x))) -> even(x) div2(|0|()) -> |0|() div2(s(|0|())) -> |0|() div2(s(s(x))) -> s(div2(x)) p(|0|()) -> |0|() p(s(x)) -> x -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: cond1#(true(),x) -> cond2#(even(x),x) p2: cond1#(true(),x) -> even#(x) p3: cond2#(true(),x) -> cond1#(neq(x,|0|()),div2(x)) p4: cond2#(true(),x) -> neq#(x,|0|()) p5: cond2#(true(),x) -> div2#(x) p6: cond2#(false(),x) -> cond1#(neq(x,|0|()),p(x)) p7: cond2#(false(),x) -> neq#(x,|0|()) p8: cond2#(false(),x) -> p#(x) p9: neq#(s(x),s(y())) -> neq#(x,y()) p10: even#(s(s(x))) -> even#(x) p11: div2#(s(s(x))) -> div2#(x) and R consists of: r1: cond1(true(),x) -> cond2(even(x),x) r2: cond2(true(),x) -> cond1(neq(x,|0|()),div2(x)) r3: cond2(false(),x) -> cond1(neq(x,|0|()),p(x)) r4: neq(|0|(),|0|()) -> false() r5: neq(|0|(),s(x)) -> true() r6: neq(s(x),|0|()) -> true() r7: neq(s(x),s(y())) -> neq(x,y()) r8: even(|0|()) -> true() r9: even(s(|0|())) -> false() r10: even(s(s(x))) -> even(x) r11: div2(|0|()) -> |0|() r12: div2(s(|0|())) -> |0|() r13: div2(s(s(x))) -> s(div2(x)) r14: p(|0|()) -> |0|() r15: p(s(x)) -> x The estimated dependency graph contains the following SCCs: {p1, p3, p6} {p10} {p11} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: cond1#(true(),x) -> cond2#(even(x),x) p2: cond2#(false(),x) -> cond1#(neq(x,|0|()),p(x)) p3: cond2#(true(),x) -> cond1#(neq(x,|0|()),div2(x)) and R consists of: r1: cond1(true(),x) -> cond2(even(x),x) r2: cond2(true(),x) -> cond1(neq(x,|0|()),div2(x)) r3: cond2(false(),x) -> cond1(neq(x,|0|()),p(x)) r4: neq(|0|(),|0|()) -> false() r5: neq(|0|(),s(x)) -> true() r6: neq(s(x),|0|()) -> true() r7: neq(s(x),s(y())) -> neq(x,y()) r8: even(|0|()) -> true() r9: even(s(|0|())) -> false() r10: even(s(s(x))) -> even(x) r11: div2(|0|()) -> |0|() r12: div2(s(|0|())) -> |0|() r13: div2(s(s(x))) -> s(div2(x)) r14: p(|0|()) -> |0|() r15: p(s(x)) -> x The set of usable rules consists of r4, r6, r8, r9, r10, r11, r12, r13, r14, r15 Take the reduction pair: max/plus interpretations on natural numbers: cond1#_A(x1,x2) = max{x1, x2 + 6} true_A = 2 cond2#_A(x1,x2) = max{x1 + 3, x2 + 6} even_A(x1) = x1 + 2 false_A = 5 neq_A(x1,x2) = max{x1 + 5, x2} |0|_A = 0 p_A(x1) = max{1, x1 - 1} div2_A(x1) = x1 s_A(x1) = x1 + 4 The next rules are strictly ordered: p2 We remove them from the problem. -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: cond1#(true(),x) -> cond2#(even(x),x) p2: cond2#(true(),x) -> cond1#(neq(x,|0|()),div2(x)) and R consists of: r1: cond1(true(),x) -> cond2(even(x),x) r2: cond2(true(),x) -> cond1(neq(x,|0|()),div2(x)) r3: cond2(false(),x) -> cond1(neq(x,|0|()),p(x)) r4: neq(|0|(),|0|()) -> false() r5: neq(|0|(),s(x)) -> true() r6: neq(s(x),|0|()) -> true() r7: neq(s(x),s(y())) -> neq(x,y()) r8: even(|0|()) -> true() r9: even(s(|0|())) -> false() r10: even(s(s(x))) -> even(x) r11: div2(|0|()) -> |0|() r12: div2(s(|0|())) -> |0|() r13: div2(s(s(x))) -> s(div2(x)) r14: p(|0|()) -> |0|() r15: p(s(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: cond1#(true(),x) -> cond2#(even(x),x) p2: cond2#(true(),x) -> cond1#(neq(x,|0|()),div2(x)) and R consists of: r1: cond1(true(),x) -> cond2(even(x),x) r2: cond2(true(),x) -> cond1(neq(x,|0|()),div2(x)) r3: cond2(false(),x) -> cond1(neq(x,|0|()),p(x)) r4: neq(|0|(),|0|()) -> false() r5: neq(|0|(),s(x)) -> true() r6: neq(s(x),|0|()) -> true() r7: neq(s(x),s(y())) -> neq(x,y()) r8: even(|0|()) -> true() r9: even(s(|0|())) -> false() r10: even(s(s(x))) -> even(x) r11: div2(|0|()) -> |0|() r12: div2(s(|0|())) -> |0|() r13: div2(s(s(x))) -> s(div2(x)) r14: p(|0|()) -> |0|() r15: p(s(x)) -> x The set of usable rules consists of r4, r6, r8, r9, r10, r11, r12, r13 Take the reduction pair: max/plus interpretations on natural numbers: cond1#_A(x1,x2) = max{x1 - 5, x2 + 1} true_A = 7 cond2#_A(x1,x2) = max{1, x1 - 8, x2 - 3} even_A(x1) = x1 + 7 neq_A(x1,x2) = max{x1 + 1, x2 + 3} |0|_A = 0 div2_A(x1) = max{0, x1 - 5} false_A = 1 s_A(x1) = max{15, x1 + 10} The next rules are strictly ordered: p1 We remove them from the problem. -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: cond2#(true(),x) -> cond1#(neq(x,|0|()),div2(x)) and R consists of: r1: cond1(true(),x) -> cond2(even(x),x) r2: cond2(true(),x) -> cond1(neq(x,|0|()),div2(x)) r3: cond2(false(),x) -> cond1(neq(x,|0|()),p(x)) r4: neq(|0|(),|0|()) -> false() r5: neq(|0|(),s(x)) -> true() r6: neq(s(x),|0|()) -> true() r7: neq(s(x),s(y())) -> neq(x,y()) r8: even(|0|()) -> true() r9: even(s(|0|())) -> false() r10: even(s(s(x))) -> even(x) r11: div2(|0|()) -> |0|() r12: div2(s(|0|())) -> |0|() r13: div2(s(s(x))) -> s(div2(x)) r14: p(|0|()) -> |0|() r15: p(s(x)) -> x The estimated dependency graph contains the following SCCs: (no SCCs) -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: even#(s(s(x))) -> even#(x) and R consists of: r1: cond1(true(),x) -> cond2(even(x),x) r2: cond2(true(),x) -> cond1(neq(x,|0|()),div2(x)) r3: cond2(false(),x) -> cond1(neq(x,|0|()),p(x)) r4: neq(|0|(),|0|()) -> false() r5: neq(|0|(),s(x)) -> true() r6: neq(s(x),|0|()) -> true() r7: neq(s(x),s(y())) -> neq(x,y()) r8: even(|0|()) -> true() r9: even(s(|0|())) -> false() r10: even(s(s(x))) -> even(x) r11: div2(|0|()) -> |0|() r12: div2(s(|0|())) -> |0|() r13: div2(s(s(x))) -> s(div2(x)) r14: p(|0|()) -> |0|() r15: p(s(x)) -> x The set of usable rules consists of (no rules) Take the monotone reduction pair: max/plus interpretations on natural numbers: even#_A(x1) = x1 s_A(x1) = x1 + 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: div2#(s(s(x))) -> div2#(x) and R consists of: r1: cond1(true(),x) -> cond2(even(x),x) r2: cond2(true(),x) -> cond1(neq(x,|0|()),div2(x)) r3: cond2(false(),x) -> cond1(neq(x,|0|()),p(x)) r4: neq(|0|(),|0|()) -> false() r5: neq(|0|(),s(x)) -> true() r6: neq(s(x),|0|()) -> true() r7: neq(s(x),s(y())) -> neq(x,y()) r8: even(|0|()) -> true() r9: even(s(|0|())) -> false() r10: even(s(s(x))) -> even(x) r11: div2(|0|()) -> |0|() r12: div2(s(|0|())) -> |0|() r13: div2(s(s(x))) -> s(div2(x)) r14: p(|0|()) -> |0|() r15: p(s(x)) -> x The set of usable rules consists of (no rules) Take the monotone reduction pair: max/plus interpretations on natural numbers: div2#_A(x1) = x1 s_A(x1) = x1 + 1 The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains.