NO Termination w.r.t. Q proof of EEG_IJCAR_12_enger-nonloop-isTrueList.ari

(0) Obligation:

Q restricted rewrite system:
The TRS R consists of the following rules:

f(tt, x) → f(isList(x), Cons(tt, x))
isList(Cons(tt, xs)) → isList(xs)
isList(nil) → tt

Q is empty.

(1) AAECC Innermost (EQUIVALENT transformation)

We have applied [NOC,AAECCNOC] to switch to innermost. The TRS R 1 is

isList(Cons(tt, xs)) → isList(xs)
isList(nil) → tt

The TRS R 2 is

f(tt, x) → f(isList(x), Cons(tt, x))

The signature Sigma is {f}

(2) Obligation:

Q restricted rewrite system:
The TRS R consists of the following rules:

f(tt, x) → f(isList(x), Cons(tt, x))
isList(Cons(tt, xs)) → isList(xs)
isList(nil) → tt

The set Q consists of the following terms:

f(tt, x0)
isList(Cons(tt, x0))
isList(nil)

(3) DependencyPairsProof (EQUIVALENT transformation)

Using Dependency Pairs [AG00,LPAR04] we result in the following initial DP problem.

(4) Obligation:

Q DP problem:
The TRS P consists of the following rules:

F(tt, x) → F(isList(x), Cons(tt, x))
F(tt, x) → ISLIST(x)
ISLIST(Cons(tt, xs)) → ISLIST(xs)

The TRS R consists of the following rules:

f(tt, x) → f(isList(x), Cons(tt, x))
isList(Cons(tt, xs)) → isList(xs)
isList(nil) → tt

The set Q consists of the following terms:

f(tt, x0)
isList(Cons(tt, x0))
isList(nil)

We have to consider all minimal (P,Q,R)-chains.

(5) DependencyGraphProof (EQUIVALENT transformation)

The approximation of the Dependency Graph [LPAR04,FROCOS05,EDGSTAR] contains 2 SCCs with 1 less node.

(6) Complex Obligation (AND)

(7) Obligation:

Q DP problem:
The TRS P consists of the following rules:

ISLIST(Cons(tt, xs)) → ISLIST(xs)

The TRS R consists of the following rules:

f(tt, x) → f(isList(x), Cons(tt, x))
isList(Cons(tt, xs)) → isList(xs)
isList(nil) → tt

The set Q consists of the following terms:

f(tt, x0)
isList(Cons(tt, x0))
isList(nil)

We have to consider all minimal (P,Q,R)-chains.

(8) UsableRulesProof (EQUIVALENT transformation)

As all Q-normal forms are R-normal forms we are in the innermost case. Hence, by the usable rules processor [LPAR04] we can delete all non-usable rules [FROCOS05] from R.

(9) Obligation:

Q DP problem:
The TRS P consists of the following rules:

ISLIST(Cons(tt, xs)) → ISLIST(xs)

R is empty.
The set Q consists of the following terms:

f(tt, x0)
isList(Cons(tt, x0))
isList(nil)

We have to consider all minimal (P,Q,R)-chains.

(10) QReductionProof (EQUIVALENT transformation)

We deleted the following terms from Q as each root-symbol of these terms does neither occur in P nor in R.[THIEMANN].

f(tt, x0)
isList(Cons(tt, x0))
isList(nil)

(11) Obligation:

Q DP problem:
The TRS P consists of the following rules:

ISLIST(Cons(tt, xs)) → ISLIST(xs)

R is empty.
Q is empty.
We have to consider all minimal (P,Q,R)-chains.

(12) QDPSizeChangeProof (EQUIVALENT transformation)

By using the subterm criterion [SUBTERM_CRITERION] together with the size-change analysis [AAECC05] we have proven that there are no infinite chains for this DP problem.

From the DPs we obtained the following set of size-change graphs:

  • ISLIST(Cons(tt, xs)) → ISLIST(xs)
    The graph contains the following edges 1 > 1

(13) YES

(14) Obligation:

Q DP problem:
The TRS P consists of the following rules:

F(tt, x) → F(isList(x), Cons(tt, x))

The TRS R consists of the following rules:

f(tt, x) → f(isList(x), Cons(tt, x))
isList(Cons(tt, xs)) → isList(xs)
isList(nil) → tt

The set Q consists of the following terms:

f(tt, x0)
isList(Cons(tt, x0))
isList(nil)

We have to consider all minimal (P,Q,R)-chains.

(15) MNOCProof (EQUIVALENT transformation)

We use the modular non-overlap check [FROCOS05] to decrease Q to the empty set.

(16) Obligation:

Q DP problem:
The TRS P consists of the following rules:

F(tt, x) → F(isList(x), Cons(tt, x))

The TRS R consists of the following rules:

f(tt, x) → f(isList(x), Cons(tt, x))
isList(Cons(tt, xs)) → isList(xs)
isList(nil) → tt

Q is empty.
We have to consider all (P,Q,R)-chains.

(17) NonLoopProof (COMPLETE transformation)

By Theorem 8 [NONLOOP] we deduce infiniteness of the QDP.
We apply the theorem with m = 1, b = 1,
σ' = [ ], and μ' = [ ] on the rule
F(tt, Cons(tt, zr0))[zr0 / Cons(tt, zr0)]n[zr0 / nil] → F(tt, Cons(tt, Cons(tt, zr0)))[zr0 / Cons(tt, zr0)]n[zr0 / nil]
This rule is correct for the QDP as the following derivation shows:

F(tt, Cons(tt, zr0))[zr0 / Cons(tt, zr0)]n[zr0 / nil] → F(tt, Cons(tt, Cons(tt, zr0)))[zr0 / Cons(tt, zr0)]n[zr0 / nil]
    by Equivalence by Domain Renaming of the lhs with [zl0 / zr0]
    intermediate steps: Equiv DR (rhs) - Equiv DR (lhs) - Equiv IPS (rhs) - Equiv IPS (lhs)
    F(tt, Cons(tt, zl1))[zr1 / Cons(tt, zr1), zl1 / Cons(tt, zl1)]n[zr1 / nil, zl1 / nil] → F(tt, Cons(tt, Cons(tt, zr1)))[zr1 / Cons(tt, zr1), zl1 / Cons(tt, zl1)]n[zr1 / nil, zl1 / nil]
        by Narrowing at position: [0]
        intermediate steps: Equiv IPS (rhs) - Equiv IPS (lhs) - Equiv IPS (rhs) - Equiv IPS (lhs) - Instantiation - Equiv DR (rhs) - Equiv DR (lhs) - Instantiation - Equiv DR (rhs) - Equiv DR (lhs)
        F(tt, Cons(tt, zs1))[zs1 / Cons(tt, zs1)]n[zs1 / y0] → F(isList(y0), Cons(tt, Cons(tt, zs1)))[zs1 / Cons(tt, zs1)]n[zs1 / y0]
            by Narrowing at position: [0]
            intermediate steps: Instantiate mu - Instantiate Sigma - Instantiation - Instantiation
            F(tt, x)[ ]n[ ] → F(isList(x), Cons(tt, x))[ ]n[ ]
                by Rule from TRS P

            intermediate steps: Equiv IPS (rhs) - Equiv IPS (rhs) - Equiv DR (lhs) - Instantiation - Equiv DR (lhs)
            isList(Cons(tt, xs))[xs / Cons(tt, xs)]n[ ] → isList(xs)[ ]n[ ]
                by PatternCreation I with delta: [ ], theta: [ ], sigma: [xs / Cons(tt, xs)]
                isList(Cons(tt, xs))[ ]n[ ] → isList(xs)[ ]n[ ]
                    by Rule from TRS R

        intermediate steps: Equiv IPS (rhs) - Equiv IPS (lhs) - Equiv IPS (rhs) - Equiv IPS (lhs)
        isList(nil)[ ]n[ ] → tt[ ]n[ ]
            by Rule from TRS R

(18) NO