0.00/0.19 YES 0.00/0.20 We consider the system theBenchmark. 0.00/0.20 0.00/0.20 Alphabet: 0.00/0.20 0.00/0.20 !plus : [nat * nat] --> nat 0.00/0.20 cons : [nat * list] --> list 0.00/0.20 map : [nat -> nat * list] --> list 0.00/0.20 nil : [] --> list 0.00/0.20 ps : [list] --> list 0.00/0.20 0.00/0.20 Rules: 0.00/0.20 0.00/0.20 map(f, nil) => nil 0.00/0.20 map(f, cons(x, y)) => cons(f x, map(f, y)) 0.00/0.20 ps(nil) => nil 0.00/0.20 ps(cons(x, y)) => cons(x, ps(map(/\z.!plus(x, z), y))) 0.00/0.20 0.00/0.20 This AFS is converted to an AFSM simply by replacing all free variables by meta-variables (with arity 0). 0.00/0.20 0.00/0.20 We use the dependency pair framework as described in [Kop12, Ch. 6/7], with static dependency pairs (see [KusIsoSakBla09] and the adaptation for AFSMs and accessible arguments in [Kop13]). 0.00/0.20 0.00/0.20 We thus obtain the following dependency pair problem (P_0, R_0, static, formative): 0.00/0.20 0.00/0.20 Dependency Pairs P_0: 0.00/0.20 0.00/0.20 0] map#(F, cons(X, Y)) =#> map#(F, Y) 0.00/0.20 1] ps#(cons(X, Y)) =#> ps#(map(/\x.!plus(X, x), Y)) 0.00/0.20 2] ps#(cons(X, Y)) =#> map#(/\x.!plus(X, x), Y) 0.00/0.20 0.00/0.20 Rules R_0: 0.00/0.20 0.00/0.20 map(F, nil) => nil 0.00/0.20 map(F, cons(X, Y)) => cons(F X, map(F, Y)) 0.00/0.20 ps(nil) => nil 0.00/0.20 ps(cons(X, Y)) => cons(X, ps(map(/\x.!plus(X, x), Y))) 0.00/0.20 0.00/0.20 Thus, the original system is terminating if (P_0, R_0, static, formative) is finite. 0.00/0.20 0.00/0.20 We consider the dependency pair problem (P_0, R_0, static, formative). 0.00/0.20 0.00/0.20 We place the elements of P in a dependency graph approximation G (see e.g. [Kop12, Thm. 7.27, 7.29], as follows: 0.00/0.20 0.00/0.20 * 0 : 0 0.00/0.20 * 1 : 1, 2 0.00/0.20 * 2 : 0 0.00/0.20 0.00/0.20 This graph has the following strongly connected components: 0.00/0.20 0.00/0.20 P_1: 0.00/0.20 0.00/0.20 map#(F, cons(X, Y)) =#> map#(F, Y) 0.00/0.20 0.00/0.20 P_2: 0.00/0.20 0.00/0.20 ps#(cons(X, Y)) =#> ps#(map(/\x.!plus(X, x), Y)) 0.00/0.20 0.00/0.20 By [Kop12, Thm. 7.31], we may replace any dependency pair problem (P_0, R_0, m, f) by (P_1, R_0, m, f) and (P_2, R_0, m, f). 0.00/0.20 0.00/0.20 Thus, the original system is terminating if each of (P_1, R_0, static, formative) and (P_2, R_0, static, formative) is finite. 0.00/0.20 0.00/0.20 We consider the dependency pair problem (P_2, R_0, static, formative). 0.00/0.20 0.00/0.20 The formative rules of (P_2, R_0) are R_1 ::= 0.00/0.20 0.00/0.20 map(F, cons(X, Y)) => cons(F X, map(F, Y)) 0.00/0.20 ps(cons(X, Y)) => cons(X, ps(map(/\x.!plus(X, x), Y))) 0.00/0.20 0.00/0.20 By [Kop12, Thm. 7.17], we may replace the dependency pair problem (P_2, R_0, static, formative) by (P_2, R_1, static, formative). 0.00/0.20 0.00/0.20 Thus, the original system is terminating if each of (P_1, R_0, static, formative) and (P_2, R_1, static, formative) is finite. 0.00/0.20 0.00/0.20 We consider the dependency pair problem (P_2, R_1, static, formative). 0.00/0.20 0.00/0.20 We will use the reduction pair processor [Kop12, Thm. 7.16]. It suffices to find a standard reduction pair [Kop12, Def. 6.69]. Thus, we must orient: 0.00/0.20 0.00/0.20 ps#(cons(X, Y)) >? ps#(map(/\x.!plus(X, x), Y)) 0.00/0.20 map(F, cons(X, Y)) >= cons(F X, map(F, Y)) 0.00/0.20 ps(cons(X, Y)) >= cons(X, ps(map(/\x.!plus(X, x), Y))) 0.00/0.20 0.00/0.20 We orient these requirements with a polynomial interpretation in the natural numbers. 0.00/0.20 0.00/0.20 The following interpretation satisfies the requirements: 0.00/0.20 0.00/0.20 !plus = \y0y1.0 0.00/0.20 cons = \y0y1.1 + y1 0.00/0.20 map = \G0y1.y1 0.00/0.20 ps = \y0.y0 0.00/0.20 ps# = \y0.2y0 0.00/0.20 0.00/0.20 Using this interpretation, the requirements translate to: 0.00/0.20 0.00/0.20 [[ps#(cons(_x0, _x1))]] = 2 + 2x1 > 2x1 = [[ps#(map(/\x.!plus(_x0, x), _x1))]] 0.00/0.20 [[map(_F0, cons(_x1, _x2))]] = 1 + x2 >= 1 + x2 = [[cons(_F0 _x1, map(_F0, _x2))]] 0.00/0.20 [[ps(cons(_x0, _x1))]] = 1 + x1 >= 1 + x1 = [[cons(_x0, ps(map(/\x.!plus(_x0, x), _x1)))]] 0.00/0.20 0.00/0.20 By the observations in [Kop12, Sec. 6.6], this reduction pair suffices; we may thus replace a dependency pair problem (P_2, R_1) by ({}, R_1). By the empty set processor [Kop12, Thm. 7.15] this problem may be immediately removed. 0.00/0.20 0.00/0.20 Thus, the original system is terminating if (P_1, R_0, static, formative) is finite. 0.00/0.20 0.00/0.20 We consider the dependency pair problem (P_1, R_0, static, formative). 0.00/0.20 0.00/0.20 We apply the subterm criterion with the following projection function: 0.00/0.20 0.00/0.20 nu(map#) = 2 0.00/0.20 0.00/0.20 Thus, we can orient the dependency pairs as follows: 0.00/0.20 0.00/0.20 nu(map#(F, cons(X, Y))) = cons(X, Y) |> Y = nu(map#(F, Y)) 0.00/0.20 0.00/0.20 By [Kop12, Thm. 7.35] and [Kop13, Thm. 5], we may replace a dependency pair problem (P_1, R_0, static, f) by ({}, R_0, static, f). By the empty set processor [Kop12, Thm. 7.15] this problem may be immediately removed. 0.00/0.20 0.00/0.20 As all dependency pair problems were succesfully simplified with sound (and complete) processors until nothing remained, we conclude termination. 0.00/0.20 0.00/0.20 0.00/0.20 +++ Citations +++ 0.00/0.20 0.00/0.20 [Kop12] C. Kop. Higher Order Termination. PhD Thesis, 2012. 0.00/0.20 [Kop13] C. Kop. Static Dependency Pairs with Accessibility. Unpublished manuscript, http://cl-informatik.uibk.ac.at/users/kop/static.pdf, 2013. 0.00/0.20 [KusIsoSakBla09] K. Kusakari, Y. Isogai, M. Sakai, and F. Blanqui. Static Dependency Pair Method Based On Strong Computability for Higher-Order Rewrite Systems. In volume 92(10) of IEICE Transactions on Information and Systems. 2007--2015, 2009. 0.00/0.20 EOF