/export/starexec/sandbox/solver/bin/starexec_run_FirstOrder /export/starexec/sandbox/benchmark/theBenchmark.xml /export/starexec/sandbox/output/output_files


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YES
We consider the system theBenchmark.

We are asked to determine termination of the following first-order TRS.

  cons : [o * o] --> o 
  empty : [] --> o 
  f : [o * o] --> o 
  g : [o * o * o] --> o 

  f(empty, X) => X 
  f(cons(X, Y), Z) => g(Y, Z, cons(X, Y)) 
  g(X, Y, Z) => f(X, cons(Y, Z)) 

We use the dependency pair framework as described in [Kop12, Ch. 6/7], with static dependency pairs (see [KusIsoSakBla09] and the adaptation for AFSMs in [Kop12, Ch. 7.8]).

We thus obtain the following dependency pair problem (P_0, R_0, minimal, formative):

  Dependency Pairs P_0:

    0] f#(cons(X, Y), Z) =#> g#(Y, Z, cons(X, Y))   
    1] g#(X, Y, Z) =#> f#(X, cons(Y, Z))   

  Rules R_0:

    f(empty, X) => X 
    f(cons(X, Y), Z) => g(Y, Z, cons(X, Y)) 
    g(X, Y, Z) => f(X, cons(Y, Z)) 

Thus, the original system is terminating if (P_0, R_0, minimal, formative) is finite.

We consider the dependency pair problem (P_0, R_0, minimal, formative).

We apply the subterm criterion with the following projection function:

  nu(f#) = 1 
  nu(g#) = 1 

Thus, we can orient the dependency pairs as follows:

  nu(f#(cons(X, Y), Z)) = cons(X, Y) |> Y = nu(g#(Y, Z, cons(X, Y))) 
  nu(g#(X, Y, Z)) = X = X = nu(f#(X, cons(Y, Z))) 

By [Kop12, Thm. 7.35], we may replace a dependency pair problem (P_0, R_0, minimal, f) by (P_1, R_0, minimal, f), where P_1 contains:

  g#(X, Y, Z) =#> f#(X, cons(Y, Z))   

Thus, the original system is terminating if (P_1, R_0, minimal, formative) is finite.

We consider the dependency pair problem (P_1, R_0, minimal, formative).

We place the elements of P in a dependency graph approximation G (see e.g. [Kop12, Thm. 7.27, 7.29], as follows:

    * 0 :  

This graph has no strongly connected components.  By [Kop12, Thm. 7.31], this implies finiteness of the dependency pair problem.

As all dependency pair problems were succesfully simplified with sound (and complete) processors until nothing remained, we conclude termination.


+++ Citations +++

[Kop12]  C. Kop.  Higher Order Termination.  PhD Thesis, 2012.
[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.