YES We show the termination of the TRS R: app(app(app(consif(),true()),x),ys) -> app(app(cons(),x),ys) app(app(app(consif(),false()),x),ys) -> ys app(app(filter(),f),nil()) -> nil() app(app(filter(),f),app(app(cons(),x),xs)) -> app(app(app(consif(),app(f,x)),x),app(app(filter(),f),xs)) Instead we prove termination of the uncurried system: app(cons_0(),y) -> cons_1(y) app(cons_1(x1),y) -> cons_2(x1,y) app(consif_0(),y) -> consif_1(y) app(consif_1(x1),y) -> consif_2(x1,y) app(consif_2(x1,x2),y) -> consif_3(x1,x2,y) app(filter_0(),y) -> filter_1(y) app(filter_1(x1),y) -> filter_2(x1,y) consif_3(true_0(),x,ys) -> cons_2(x,ys) consif_3(false_0(),x,ys) -> ys filter_2(f,nil_0()) -> nil_0() filter_2(f,cons_2(x,xs)) -> consif_3(app(f,x),x,filter_2(f,xs)) -- SCC decomposition. Consider the dependency pair problem (P, R), where P consists of p1: app#(consif_2(x1,x2),y) -> consif_3#(x1,x2,y) p2: app#(filter_1(x1),y) -> filter_2#(x1,y) p3: filter_2#(f,cons_2(x,xs)) -> consif_3#(app(f,x),x,filter_2(f,xs)) p4: filter_2#(f,cons_2(x,xs)) -> app#(f,x) p5: filter_2#(f,cons_2(x,xs)) -> filter_2#(f,xs) and R consists of: r1: app(cons_0(),y) -> cons_1(y) r2: app(cons_1(x1),y) -> cons_2(x1,y) r3: app(consif_0(),y) -> consif_1(y) r4: app(consif_1(x1),y) -> consif_2(x1,y) r5: app(consif_2(x1,x2),y) -> consif_3(x1,x2,y) r6: app(filter_0(),y) -> filter_1(y) r7: app(filter_1(x1),y) -> filter_2(x1,y) r8: consif_3(true_0(),x,ys) -> cons_2(x,ys) r9: consif_3(false_0(),x,ys) -> ys r10: filter_2(f,nil_0()) -> nil_0() r11: filter_2(f,cons_2(x,xs)) -> consif_3(app(f,x),x,filter_2(f,xs)) The estimated dependency graph contains the following SCCs: {p2, p4, p5} -- Reduction pair. Consider the dependency pair problem (P, R), where P consists of p1: app#(filter_1(x1),y) -> filter_2#(x1,y) p2: filter_2#(f,cons_2(x,xs)) -> filter_2#(f,xs) p3: filter_2#(f,cons_2(x,xs)) -> app#(f,x) and R consists of: r1: app(cons_0(),y) -> cons_1(y) r2: app(cons_1(x1),y) -> cons_2(x1,y) r3: app(consif_0(),y) -> consif_1(y) r4: app(consif_1(x1),y) -> consif_2(x1,y) r5: app(consif_2(x1,x2),y) -> consif_3(x1,x2,y) r6: app(filter_0(),y) -> filter_1(y) r7: app(filter_1(x1),y) -> filter_2(x1,y) r8: consif_3(true_0(),x,ys) -> cons_2(x,ys) r9: consif_3(false_0(),x,ys) -> ys r10: filter_2(f,nil_0()) -> nil_0() r11: filter_2(f,cons_2(x,xs)) -> consif_3(app(f,x),x,filter_2(f,xs)) The set of usable rules consists of (no rules) Take the reduction pair: generalized weighted path order (>=MG, >G) base order 1: max/plus interpretation on natural numbers: app#_A(x1,x2) = max{4, x1 - 1} filter_1_A(x1) = max{10, x1 + 7} filter_2#_A(x1,x2) = max{8, x1 + 5} cons_2_A(x1,x2) = max{3, x1 - 20, x2 - 20} base order 2: marked-algebra reduction triple (>=A, >=A!, >A!): max/plus interpretation on natural numbers: app#_A(x1,x2) = max{0, x1 - 13, x2 - 25} filter_1_A(x1) = x1 + 12 filter_2#_A(x1,x2) = max{0, x1 - 13, x2 - 25} cons_2_A(x1,x2) = max{24, x1 + 14, x2 + 17} app#!_A(x1,x2) = max{9, x1 - 13, x2 - 1} filter_1!_A(x1) = 8 filter_2#!_A(x1,x2) = max{7, x2 - 16} cons_2!_A(x1,x2) = max{7, x1 - 13, x2 - 16} partial status: pi(app#) = [] pi(filter_1) = [1] pi(filter_2#) = [] pi(cons_2) = [] The following rules are removed: p1, p2, p3 Then no dependency pair remains.