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

(0) Obligation:

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

while(true, x, y) → while(lt(x, y), s(x), s(y))
lt(s(x), s(y)) → lt(x, y)
lt(0, y) → true

Q is empty.

(1) AAECC Innermost (EQUIVALENT transformation)

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

lt(s(x), s(y)) → lt(x, y)
lt(0, y) → true

The TRS R 2 is

while(true, x, y) → while(lt(x, y), s(x), s(y))

The signature Sigma is {while}

(2) Obligation:

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

while(true, x, y) → while(lt(x, y), s(x), s(y))
lt(s(x), s(y)) → lt(x, y)
lt(0, y) → true

The set Q consists of the following terms:

while(true, x0, x1)
lt(s(x0), s(x1))
lt(0, x0)

(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:

WHILE(true, x, y) → WHILE(lt(x, y), s(x), s(y))
WHILE(true, x, y) → LT(x, y)
LT(s(x), s(y)) → LT(x, y)

The TRS R consists of the following rules:

while(true, x, y) → while(lt(x, y), s(x), s(y))
lt(s(x), s(y)) → lt(x, y)
lt(0, y) → true

The set Q consists of the following terms:

while(true, x0, x1)
lt(s(x0), s(x1))
lt(0, x0)

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:

LT(s(x), s(y)) → LT(x, y)

The TRS R consists of the following rules:

while(true, x, y) → while(lt(x, y), s(x), s(y))
lt(s(x), s(y)) → lt(x, y)
lt(0, y) → true

The set Q consists of the following terms:

while(true, x0, x1)
lt(s(x0), s(x1))
lt(0, x0)

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:

LT(s(x), s(y)) → LT(x, y)

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

while(true, x0, x1)
lt(s(x0), s(x1))
lt(0, x0)

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].

while(true, x0, x1)
lt(s(x0), s(x1))
lt(0, x0)

(11) Obligation:

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

LT(s(x), s(y)) → LT(x, y)

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:

  • LT(s(x), s(y)) → LT(x, y)
    The graph contains the following edges 1 > 1, 2 > 2

(13) YES

(14) Obligation:

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

WHILE(true, x, y) → WHILE(lt(x, y), s(x), s(y))

The TRS R consists of the following rules:

while(true, x, y) → while(lt(x, y), s(x), s(y))
lt(s(x), s(y)) → lt(x, y)
lt(0, y) → true

The set Q consists of the following terms:

while(true, x0, x1)
lt(s(x0), s(x1))
lt(0, x0)

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:

WHILE(true, x, y) → WHILE(lt(x, y), s(x), s(y))

The TRS R consists of the following rules:

while(true, x, y) → while(lt(x, y), s(x), s(y))
lt(s(x), s(y)) → lt(x, y)
lt(0, y) → true

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
WHILE(true, s(zr0), s(zr1))[zr0 / s(zr0), zr1 / s(zr1)]n[zr0 / 0] → WHILE(true, s(s(zr0)), s(s(zr1)))[zr0 / s(zr0), zr1 / s(zr1)]n[zr0 / 0]
This rule is correct for the QDP as the following derivation shows:

WHILE(true, s(zr0), s(zr1))[zr0 / s(zr0), zr1 / s(zr1)]n[zr0 / 0] → WHILE(true, s(s(zr0)), s(s(zr1)))[zr0 / s(zr0), zr1 / s(zr1)]n[zr0 / 0]
    by Equivalence by Irrelevant Pattern Substitutions σ: [zr0 / s(zr0), zr1 / s(zr1)] µ: [zr0 / 0]
    intermediate steps: Equiv IPS (lhs) - Instantiate mu - Equiv DR (lhs) - Instantiation - Equiv DR (rhs) - Equiv DR (lhs) - Equiv IPS (rhs) - Equiv IPS (lhs)
    WHILE(true, s(zl2), s(zl3))[zr2 / s(zr2), zr3 / s(zr3), zl2 / s(zl2), zl3 / s(zl3)]n[zr2 / 0, zr3 / x1, zl2 / 0, zl3 / x1] → WHILE(true, s(s(zr2)), s(s(zr3)))[zr2 / s(zr2), zr3 / s(zr3), zl2 / s(zl2), zl3 / s(zl3)]n[zr2 / 0, zr3 / x1, zl2 / 0, zl3 / x1]
        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)
        WHILE(true, s(zs2), s(zs3))[zs2 / s(zs2), zs3 / s(zs3)]n[zs2 / y1, zs3 / y0] → WHILE(lt(y1, y0), s(s(zs2)), s(s(zs3)))[zs2 / s(zs2), zs3 / s(zs3)]n[zs2 / y1, zs3 / y0]
            by Narrowing at position: [0]
            intermediate steps: Instantiate mu - Instantiate Sigma - Instantiation - Instantiation - Instantiation
            WHILE(true, x, y)[ ]n[ ] → WHILE(lt(x, y), s(x), s(y))[ ]n[ ]
                by Rule from TRS P

            intermediate steps: Equiv IPS (rhs) - Equiv IPS (rhs) - Instantiation - Equiv DR (lhs) - Instantiation - Equiv DR (lhs)
            lt(s(x), s(y))[x / s(x), y / s(y)]n[ ] → lt(x, y)[ ]n[ ]
                by PatternCreation I with delta: [ ], theta: [ ], sigma: [x / s(x), y / s(y)]
                lt(s(x), s(y))[ ]n[ ] → lt(x, y)[ ]n[ ]
                    by Rule from TRS R

        intermediate steps: Equiv IPS (rhs) - Equiv IPS (lhs) - Equiv IPS (rhs) - Equiv IPS (lhs) - Instantiation - Instantiation
        lt(0, y)[ ]n[ ] → true[ ]n[ ]
            by Rule from TRS R

(18) NO