YES We show the termination of the TRS R: app(id(),x) -> x app(add(),|0|()) -> id() app(app(add(),app(s(),x)),y) -> app(s(),app(app(add(),x),y)) app(app(map(),f),nil()) -> nil() app(app(map(),f),app(app(cons(),x),xs)) -> app(app(cons(),app(f,x)),app(app(map(),f),xs)) -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: app#(app(add(),app(s(),x)),y) -> app#(s(),app(app(add(),x),y)) p2: app#(app(add(),app(s(),x)),y) -> app#(app(add(),x),y) p3: app#(app(add(),app(s(),x)),y) -> app#(add(),x) p4: app#(app(map(),f),app(app(cons(),x),xs)) -> app#(app(cons(),app(f,x)),app(app(map(),f),xs)) p5: app#(app(map(),f),app(app(cons(),x),xs)) -> app#(cons(),app(f,x)) p6: app#(app(map(),f),app(app(cons(),x),xs)) -> app#(f,x) p7: app#(app(map(),f),app(app(cons(),x),xs)) -> app#(app(map(),f),xs) and R consists of: r1: app(id(),x) -> x r2: app(add(),|0|()) -> id() r3: app(app(add(),app(s(),x)),y) -> app(s(),app(app(add(),x),y)) r4: app(app(map(),f),nil()) -> nil() r5: app(app(map(),f),app(app(cons(),x),xs)) -> app(app(cons(),app(f,x)),app(app(map(),f),xs)) The estimated dependency graph contains the following SCCs: {p2, p6, p7} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: app#(app(add(),app(s(),x)),y) -> app#(app(add(),x),y) p2: app#(app(map(),f),app(app(cons(),x),xs)) -> app#(app(map(),f),xs) p3: app#(app(map(),f),app(app(cons(),x),xs)) -> app#(f,x) and R consists of: r1: app(id(),x) -> x r2: app(add(),|0|()) -> id() r3: app(app(add(),app(s(),x)),y) -> app(s(),app(app(add(),x),y)) r4: app(app(map(),f),nil()) -> nil() r5: app(app(map(),f),app(app(cons(),x),xs)) -> app(app(cons(),app(f,x)),app(app(map(),f),xs)) The set of usable rules consists of r2 Take the reduction pair: lexicographic combination of reduction pairs: 1. weighted path order base order: max/plus interpretations on natural numbers: app#_A(x1,x2) = max{x1 + 3, x2 + 14} app_A(x1,x2) = max{x1 + 9, x2 + 4} add_A = 3 s_A = 4 map_A = 2 cons_A = 0 |0|_A = 3 id_A = 2 precedence: app# = add = s = map = cons > id > app = |0| partial status: pi(app#) = [1, 2] pi(app) = [1, 2] pi(add) = [] pi(s) = [] pi(map) = [] pi(cons) = [] pi(|0|) = [] pi(id) = [] 2. weighted path order base order: max/plus interpretations on natural numbers: app#_A(x1,x2) = max{x1 + 4, x2 + 8} app_A(x1,x2) = max{x1 + 2, x2 + 5} add_A = 2 s_A = 1 map_A = 2 cons_A = 1 |0|_A = 2 id_A = 3 precedence: app# > app > map > cons = id > add = s = |0| partial status: pi(app#) = [1, 2] pi(app) = [] pi(add) = [] pi(s) = [] pi(map) = [] pi(cons) = [] pi(|0|) = [] pi(id) = [] The next rules are strictly ordered: p1, p2, p3 We remove them from the problem. Then no dependency pair remains.