YES We show the termination of the TRS R: cond1(true(),x,y) -> cond2(gr(y,|0|()),x,y) cond2(true(),x,y) -> cond2(gr(y,|0|()),x,p(y)) cond2(false(),x,y) -> cond1(gr(x,|0|()),p(x),y) gr(|0|(),x) -> false() gr(s(x),|0|()) -> true() gr(s(x),s(y)) -> gr(x,y) p(|0|()) -> |0|() p(s(x)) -> x -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: cond1#(true(),x,y) -> cond2#(gr(y,|0|()),x,y) p2: cond1#(true(),x,y) -> gr#(y,|0|()) p3: cond2#(true(),x,y) -> cond2#(gr(y,|0|()),x,p(y)) p4: cond2#(true(),x,y) -> gr#(y,|0|()) p5: cond2#(true(),x,y) -> p#(y) p6: cond2#(false(),x,y) -> cond1#(gr(x,|0|()),p(x),y) p7: cond2#(false(),x,y) -> gr#(x,|0|()) p8: cond2#(false(),x,y) -> p#(x) p9: gr#(s(x),s(y)) -> gr#(x,y) and R consists of: r1: cond1(true(),x,y) -> cond2(gr(y,|0|()),x,y) r2: cond2(true(),x,y) -> cond2(gr(y,|0|()),x,p(y)) r3: cond2(false(),x,y) -> cond1(gr(x,|0|()),p(x),y) r4: gr(|0|(),x) -> false() r5: gr(s(x),|0|()) -> true() r6: gr(s(x),s(y)) -> gr(x,y) r7: p(|0|()) -> |0|() r8: p(s(x)) -> x The estimated dependency graph contains the following SCCs: {p1, p3, p6} {p9} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: cond1#(true(),x,y) -> cond2#(gr(y,|0|()),x,y) p2: cond2#(false(),x,y) -> cond1#(gr(x,|0|()),p(x),y) p3: cond2#(true(),x,y) -> cond2#(gr(y,|0|()),x,p(y)) and R consists of: r1: cond1(true(),x,y) -> cond2(gr(y,|0|()),x,y) r2: cond2(true(),x,y) -> cond2(gr(y,|0|()),x,p(y)) r3: cond2(false(),x,y) -> cond1(gr(x,|0|()),p(x),y) r4: gr(|0|(),x) -> false() r5: gr(s(x),|0|()) -> true() r6: gr(s(x),s(y)) -> gr(x,y) r7: p(|0|()) -> |0|() r8: p(s(x)) -> x The set of usable rules consists of r4, r5, r7, r8 Take the reduction pair: lexicographic combination of reduction pairs: 1. weighted path order base order: max/plus interpretations on natural numbers: cond1#_A(x1,x2,x3) = max{x1 + 4, x2 + 15} true_A = 12 cond2#_A(x1,x2,x3) = max{15, x2 + 14} gr_A(x1,x2) = max{x1 + 8, x2 + 6} |0|_A = 0 false_A = 3 p_A(x1) = max{0, x1 - 2} s_A(x1) = max{14, x1 + 13} precedence: cond2# = gr = p = s > cond1# > true = |0| = false partial status: pi(cond1#) = [1] pi(true) = [] pi(cond2#) = [] pi(gr) = [] pi(|0|) = [] pi(false) = [] pi(p) = [] pi(s) = [] 2. weighted path order base order: max/plus interpretations on natural numbers: cond1#_A(x1,x2,x3) = x1 true_A = 7 cond2#_A(x1,x2,x3) = 3 gr_A(x1,x2) = 2 |0|_A = 6 false_A = 1 p_A(x1) = 0 s_A(x1) = 0 precedence: |0| > cond1# = cond2# = p = s > true > gr > false partial status: pi(cond1#) = [1] pi(true) = [] pi(cond2#) = [] pi(gr) = [] pi(|0|) = [] pi(false) = [] pi(p) = [] pi(s) = [] 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,y) -> cond2#(gr(y,|0|()),x,y) p2: cond2#(true(),x,y) -> cond2#(gr(y,|0|()),x,p(y)) and R consists of: r1: cond1(true(),x,y) -> cond2(gr(y,|0|()),x,y) r2: cond2(true(),x,y) -> cond2(gr(y,|0|()),x,p(y)) r3: cond2(false(),x,y) -> cond1(gr(x,|0|()),p(x),y) r4: gr(|0|(),x) -> false() r5: gr(s(x),|0|()) -> true() r6: gr(s(x),s(y)) -> gr(x,y) r7: p(|0|()) -> |0|() r8: p(s(x)) -> x The estimated dependency graph contains the following SCCs: {p2} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: cond2#(true(),x,y) -> cond2#(gr(y,|0|()),x,p(y)) and R consists of: r1: cond1(true(),x,y) -> cond2(gr(y,|0|()),x,y) r2: cond2(true(),x,y) -> cond2(gr(y,|0|()),x,p(y)) r3: cond2(false(),x,y) -> cond1(gr(x,|0|()),p(x),y) r4: gr(|0|(),x) -> false() r5: gr(s(x),|0|()) -> true() r6: gr(s(x),s(y)) -> gr(x,y) r7: p(|0|()) -> |0|() r8: p(s(x)) -> x The set of usable rules consists of r4, r5, r7, r8 Take the reduction pair: lexicographic combination of reduction pairs: 1. weighted path order base order: max/plus interpretations on natural numbers: cond2#_A(x1,x2,x3) = max{12, x1, x3 + 5} true_A = 13 gr_A(x1,x2) = max{x1 + 2, x2 + 3} |0|_A = 1 p_A(x1) = max{6, x1 - 1} false_A = 2 s_A(x1) = x1 + 14 precedence: cond2# = true = gr = |0| = p = false = s partial status: pi(cond2#) = [1, 3] pi(true) = [] pi(gr) = [1, 2] pi(|0|) = [] pi(p) = [] pi(false) = [] pi(s) = [1] 2. weighted path order base order: max/plus interpretations on natural numbers: cond2#_A(x1,x2,x3) = max{x1 + 2, x3 + 3} true_A = 1 gr_A(x1,x2) = max{x1 + 4, x2 + 6} |0|_A = 2 p_A(x1) = 4 false_A = 5 s_A(x1) = x1 + 2 precedence: cond2# = true = gr = |0| = p = false = s partial status: pi(cond2#) = [3] pi(true) = [] pi(gr) = [1, 2] pi(|0|) = [] pi(p) = [] pi(false) = [] pi(s) = [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: gr#(s(x),s(y)) -> gr#(x,y) and R consists of: r1: cond1(true(),x,y) -> cond2(gr(y,|0|()),x,y) r2: cond2(true(),x,y) -> cond2(gr(y,|0|()),x,p(y)) r3: cond2(false(),x,y) -> cond1(gr(x,|0|()),p(x),y) r4: gr(|0|(),x) -> false() r5: gr(s(x),|0|()) -> true() r6: gr(s(x),s(y)) -> gr(x,y) r7: p(|0|()) -> |0|() r8: p(s(x)) -> x The set of usable rules consists of (no rules) Take the reduction pair: lexicographic combination of reduction pairs: 1. weighted path order base order: max/plus interpretations on natural numbers: gr#_A(x1,x2) = max{2, x1 - 1, x2 + 1} s_A(x1) = max{1, x1} precedence: gr# = s partial status: pi(gr#) = [2] pi(s) = [1] 2. weighted path order base order: max/plus interpretations on natural numbers: gr#_A(x1,x2) = 0 s_A(x1) = max{2, x1} precedence: gr# = s partial status: pi(gr#) = [] pi(s) = [1] The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains.