YES We show the termination of the TRS R: plus(x,|0|()) -> x plus(x,s(y)) -> s(plus(x,y)) times(|0|(),y) -> |0|() times(x,|0|()) -> |0|() times(s(x),y) -> plus(times(x,y),y) p(s(s(x))) -> s(p(s(x))) p(s(|0|())) -> |0|() fac(s(x)) -> times(fac(p(s(x))),s(x)) -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: plus#(x,s(y)) -> plus#(x,y) p2: times#(s(x),y) -> plus#(times(x,y),y) p3: times#(s(x),y) -> times#(x,y) p4: p#(s(s(x))) -> p#(s(x)) p5: fac#(s(x)) -> times#(fac(p(s(x))),s(x)) p6: fac#(s(x)) -> fac#(p(s(x))) p7: fac#(s(x)) -> p#(s(x)) and R consists of: r1: plus(x,|0|()) -> x r2: plus(x,s(y)) -> s(plus(x,y)) r3: times(|0|(),y) -> |0|() r4: times(x,|0|()) -> |0|() r5: times(s(x),y) -> plus(times(x,y),y) r6: p(s(s(x))) -> s(p(s(x))) r7: p(s(|0|())) -> |0|() r8: fac(s(x)) -> times(fac(p(s(x))),s(x)) The estimated dependency graph contains the following SCCs: {p6} {p3} {p1} {p4} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: fac#(s(x)) -> fac#(p(s(x))) and R consists of: r1: plus(x,|0|()) -> x r2: plus(x,s(y)) -> s(plus(x,y)) r3: times(|0|(),y) -> |0|() r4: times(x,|0|()) -> |0|() r5: times(s(x),y) -> plus(times(x,y),y) r6: p(s(s(x))) -> s(p(s(x))) r7: p(s(|0|())) -> |0|() r8: fac(s(x)) -> times(fac(p(s(x))),s(x)) The set of usable rules consists of r6, r7 Take the reduction pair: lexicographic combination of reduction pairs: 1. weighted path order base order: max/plus interpretations on natural numbers: fac#_A(x1) = max{5, x1 + 3} s_A(x1) = x1 + 13 p_A(x1) = max{8, x1 - 5} |0|_A = 7 precedence: fac# = p > |0| > s partial status: pi(fac#) = [1] pi(s) = [] pi(p) = [] pi(|0|) = [] 2. weighted path order base order: max/plus interpretations on natural numbers: fac#_A(x1) = 0 s_A(x1) = 6 p_A(x1) = 11 |0|_A = 6 precedence: s > |0| > fac# = p partial status: pi(fac#) = [] pi(s) = [] pi(p) = [] pi(|0|) = [] 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: times#(s(x),y) -> times#(x,y) and R consists of: r1: plus(x,|0|()) -> x r2: plus(x,s(y)) -> s(plus(x,y)) r3: times(|0|(),y) -> |0|() r4: times(x,|0|()) -> |0|() r5: times(s(x),y) -> plus(times(x,y),y) r6: p(s(s(x))) -> s(p(s(x))) r7: p(s(|0|())) -> |0|() r8: fac(s(x)) -> times(fac(p(s(x))),s(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: times#_A(x1,x2) = max{2, x1 + 1, x2} s_A(x1) = max{1, x1} precedence: times# = s partial status: pi(times#) = [1, 2] pi(s) = [1] 2. weighted path order base order: max/plus interpretations on natural numbers: times#_A(x1,x2) = x2 + 1 s_A(x1) = x1 + 1 precedence: times# = s partial status: pi(times#) = [] 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: plus#(x,s(y)) -> plus#(x,y) and R consists of: r1: plus(x,|0|()) -> x r2: plus(x,s(y)) -> s(plus(x,y)) r3: times(|0|(),y) -> |0|() r4: times(x,|0|()) -> |0|() r5: times(s(x),y) -> plus(times(x,y),y) r6: p(s(s(x))) -> s(p(s(x))) r7: p(s(|0|())) -> |0|() r8: fac(s(x)) -> times(fac(p(s(x))),s(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: plus#_A(x1,x2) = max{2, x1, x2 + 1} s_A(x1) = max{1, x1} precedence: plus# = s partial status: pi(plus#) = [1, 2] pi(s) = [1] 2. weighted path order base order: max/plus interpretations on natural numbers: plus#_A(x1,x2) = max{x1, x2 - 1} s_A(x1) = x1 precedence: plus# = s partial status: pi(plus#) = [1] 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: p#(s(s(x))) -> p#(s(x)) and R consists of: r1: plus(x,|0|()) -> x r2: plus(x,s(y)) -> s(plus(x,y)) r3: times(|0|(),y) -> |0|() r4: times(x,|0|()) -> |0|() r5: times(s(x),y) -> plus(times(x,y),y) r6: p(s(s(x))) -> s(p(s(x))) r7: p(s(|0|())) -> |0|() r8: fac(s(x)) -> times(fac(p(s(x))),s(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: p#_A(x1) = x1 + 1 s_A(x1) = x1 precedence: p# = s partial status: pi(p#) = [] pi(s) = [] 2. weighted path order base order: max/plus interpretations on natural numbers: p#_A(x1) = x1 + 3 s_A(x1) = x1 + 1 precedence: p# > s partial status: pi(p#) = [] pi(s) = [1] The next rules are strictly ordered: p1 We remove them from the problem. Then no dependency pair remains.