0.00/0.08 YES 0.00/0.08 We consider the system theBenchmark. 0.00/0.08 0.00/0.08 Alphabet: 0.00/0.08 0.00/0.08 0 : [] --> b 0.00/0.08 cons : [b * a] --> a 0.00/0.08 curry : [b -> b -> b * b] --> b -> b 0.00/0.08 inc : [] --> a -> a 0.00/0.08 map : [b -> b] --> a -> a 0.00/0.08 nil : [] --> a 0.00/0.08 plus : [] --> b -> b -> b 0.00/0.08 s : [b] --> b 0.00/0.08 0.00/0.08 Rules: 0.00/0.08 0.00/0.08 plus 0 x => x 0.00/0.08 plus s(x) y => s(plus x y) 0.00/0.08 map(f) nil => nil 0.00/0.08 map(f) cons(x, y) => cons(f x, map(f) y) 0.00/0.08 curry(f, x) y => f x y 0.00/0.08 inc => map(curry(plus, s(0))) 0.00/0.08 0.00/0.08 This AFS is converted to an AFSM simply by replacing all free variables by meta-variables (with arity 0). 0.00/0.08 0.00/0.08 Symbol curry is an encoding for application that is only used in innocuous ways. We can simplify the program (without losing non-termination) by removing it. This gives: 0.00/0.08 0.00/0.08 Alphabet: 0.00/0.08 0.00/0.08 0 : [] --> b 0.00/0.08 cons : [b * a] --> a 0.00/0.08 inc : [] --> a -> a 0.00/0.08 map : [b -> b] --> a -> a 0.00/0.08 nil : [] --> a 0.00/0.08 plus : [b] --> b -> b 0.00/0.08 s : [b] --> b 0.00/0.08 0.00/0.08 Rules: 0.00/0.08 0.00/0.08 plus(0) X => X 0.00/0.08 plus(s(X)) Y => s(plus(X) Y) 0.00/0.08 map(F) nil => nil 0.00/0.08 map(F) cons(X, Y) => cons(F X, map(F) Y) 0.00/0.08 inc => map(plus(s(0))) 0.00/0.08 0.00/0.08 We use rule removal, following [Kop12, Theorem 2.23]. 0.00/0.08 0.00/0.08 This gives the following requirements (possibly using Theorems 2.25 and 2.26 in [Kop12]): 0.00/0.08 0.00/0.08 plus(0) X >? X 0.00/0.08 plus(s(X)) Y >? s(plus(X) Y) 0.00/0.08 map(F) nil >? nil 0.00/0.08 map(F) cons(X, Y) >? cons(F X, map(F) Y) 0.00/0.08 inc >? map(plus(s(0))) 0.00/0.08 0.00/0.08 We orient these requirements with a polynomial interpretation in the natural numbers. 0.00/0.08 0.00/0.08 The following interpretation satisfies the requirements: 0.00/0.08 0.00/0.08 0 = 0 0.00/0.08 cons = \y0y1.3 + y0 + y1 0.00/0.08 inc = \y0.3 + 3y0 0.00/0.08 map = \G0y1.G0(0) + y1G0(y1) 0.00/0.08 nil = 3 0.00/0.08 plus = \y0y1.2y0 0.00/0.08 s = \y0.1 + y0 0.00/0.08 0.00/0.08 Using this interpretation, the requirements translate to: 0.00/0.08 0.00/0.08 [[plus(0) _x0]] = x0 >= x0 = [[_x0]] 0.00/0.08 [[plus(s(_x0)) _x1]] = 2 + x1 + 2x0 > 1 + x1 + 2x0 = [[s(plus(_x0) _x1)]] 0.00/0.08 [[map(_F0) nil]] = 3 + F0(0) + 3F0(3) >= 3 = [[nil]] 0.00/0.08 [[map(_F0) cons(_x1, _x2)]] = 3 + x1 + x2 + F0(0) + 3F0(3 + x1 + x2) + x1F0(3 + x1 + x2) + x2F0(3 + x1 + x2) >= 3 + x1 + x2 + F0(0) + F0(x1) + x2F0(x2) = [[cons(_F0 _x1, map(_F0) _x2)]] 0.00/0.09 [[inc]] = \y0.3 + 3y0 > \y0.2 + 2y0 = [[map(plus(s(0)))]] 0.00/0.09 0.00/0.09 We can thus remove the following rules: 0.00/0.09 0.00/0.09 plus(s(X)) Y => s(plus(X) Y) 0.00/0.09 inc => map(plus(s(0))) 0.00/0.09 0.00/0.09 We use rule removal, following [Kop12, Theorem 2.23]. 0.00/0.09 0.00/0.09 This gives the following requirements (possibly using Theorems 2.25 and 2.26 in [Kop12]): 0.00/0.09 0.00/0.09 plus(0, X) >? X 0.00/0.09 map(F, nil) >? nil 0.00/0.09 map(F, cons(X, Y)) >? cons(F X, map(F, Y)) 0.00/0.09 0.00/0.09 We orient these requirements with a polynomial interpretation in the natural numbers. 0.00/0.09 0.00/0.09 The following interpretation satisfies the requirements: 0.00/0.09 0.00/0.09 0 = 3 0.00/0.09 cons = \y0y1.3 + y0 + y1 0.00/0.09 map = \G0y1.3 + 3y1 + 2G0(0) + 2G0(y1) + 3y1G0(y1) 0.00/0.09 nil = 0 0.00/0.09 plus = \y0y1.3 + y0 + y1 0.00/0.09 0.00/0.09 Using this interpretation, the requirements translate to: 0.00/0.09 0.00/0.09 [[plus(0, _x0)]] = 6 + x0 > x0 = [[_x0]] 0.00/0.09 [[map(_F0, nil)]] = 3 + 4F0(0) > 0 = [[nil]] 0.00/0.09 [[map(_F0, cons(_x1, _x2))]] = 12 + 3x1 + 3x2 + 2F0(0) + 3x1F0(3 + x1 + x2) + 3x2F0(3 + x1 + x2) + 11F0(3 + x1 + x2) > 6 + x1 + 3x2 + F0(x1) + 2F0(0) + 2F0(x2) + 3x2F0(x2) = [[cons(_F0 _x1, map(_F0, _x2))]] 0.00/0.09 0.00/0.09 We can thus remove the following rules: 0.00/0.09 0.00/0.09 plus(0, X) => X 0.00/0.09 map(F, nil) => nil 0.00/0.09 map(F, cons(X, Y)) => cons(F X, map(F, Y)) 0.00/0.09 0.00/0.09 All rules were succesfully removed. Thus, termination of the original system has been reduced to termination of the beta-rule, which is well-known to hold. 0.00/0.09 0.00/0.09 0.00/0.09 +++ Citations +++ 0.00/0.09 0.00/0.09 [Kop12] C. Kop. Higher Order Termination. PhD Thesis, 2012. 0.00/0.09 EOF