(0) Obligation:

Clauses:

countstack(empty, 0).
countstack(S, X) :- ','(no(empty_stack(S)), ','(pop(S, nil), ','(popped(S, Pd), countstack(Pd, X)))).
countstack(S, s(X)) :- ','(no(empty_stack(S)), ','(pop(S, P), ','(no(empty_list(P)), ','(head(P, H), ','(tail(P, T), ','(popped(S, Pd), countstack(push(H, push(T, Pd)), X))))))).
pop(empty, X1).
pop(push(P, X2), P).
popped(empty, empty).
popped(push(X3, Pd), Pd).
head(nil, X4).
head(cons(H, X5), H).
tail(nil, nil).
tail(cons(X6, T), T).
empty_stack(empty).
empty_list(nil).
no(X) :- ','(X, ','(!, failure(a))).
no(X7).
failure(b).

Query: countstack(g,a)

(1) PrologToPiTRSViaGraphTransformerProof (SOUND transformation)

Transformed Prolog program to (Pi-)TRS.

(2) Obligation:

Pi-finite rewrite system:
The TRS R consists of the following rules:

countstackA_in_ga(empty, 0) → countstackA_out_ga(empty, 0)
countstackA_in_ga(push(nil, T35), T14) → U1_ga(T35, T14, countstackA_in_ga(T35, T14))
countstackA_in_ga(push(cons(T79, T80), T81), s(T42)) → U2_ga(T79, T80, T81, T42, countstackA_in_ga(push(T79, push(T80, T81)), T42))
U2_ga(T79, T80, T81, T42, countstackA_out_ga(push(T79, push(T80, T81)), T42)) → countstackA_out_ga(push(cons(T79, T80), T81), s(T42))
U1_ga(T35, T14, countstackA_out_ga(T35, T14)) → countstackA_out_ga(push(nil, T35), T14)

The argument filtering Pi contains the following mapping:
countstackA_in_ga(x1, x2)  =  countstackA_in_ga(x1)
empty  =  empty
countstackA_out_ga(x1, x2)  =  countstackA_out_ga(x1, x2)
push(x1, x2)  =  push(x1, x2)
nil  =  nil
U1_ga(x1, x2, x3)  =  U1_ga(x1, x3)
cons(x1, x2)  =  cons(x1, x2)
U2_ga(x1, x2, x3, x4, x5)  =  U2_ga(x1, x2, x3, x5)
s(x1)  =  s(x1)

(3) DependencyPairsProof (EQUIVALENT transformation)

Using Dependency Pairs [AG00,LOPSTR] we result in the following initial DP problem:
Pi DP problem:
The TRS P consists of the following rules:

COUNTSTACKA_IN_GA(push(nil, T35), T14) → U1_GA(T35, T14, countstackA_in_ga(T35, T14))
COUNTSTACKA_IN_GA(push(nil, T35), T14) → COUNTSTACKA_IN_GA(T35, T14)
COUNTSTACKA_IN_GA(push(cons(T79, T80), T81), s(T42)) → U2_GA(T79, T80, T81, T42, countstackA_in_ga(push(T79, push(T80, T81)), T42))
COUNTSTACKA_IN_GA(push(cons(T79, T80), T81), s(T42)) → COUNTSTACKA_IN_GA(push(T79, push(T80, T81)), T42)

The TRS R consists of the following rules:

countstackA_in_ga(empty, 0) → countstackA_out_ga(empty, 0)
countstackA_in_ga(push(nil, T35), T14) → U1_ga(T35, T14, countstackA_in_ga(T35, T14))
countstackA_in_ga(push(cons(T79, T80), T81), s(T42)) → U2_ga(T79, T80, T81, T42, countstackA_in_ga(push(T79, push(T80, T81)), T42))
U2_ga(T79, T80, T81, T42, countstackA_out_ga(push(T79, push(T80, T81)), T42)) → countstackA_out_ga(push(cons(T79, T80), T81), s(T42))
U1_ga(T35, T14, countstackA_out_ga(T35, T14)) → countstackA_out_ga(push(nil, T35), T14)

The argument filtering Pi contains the following mapping:
countstackA_in_ga(x1, x2)  =  countstackA_in_ga(x1)
empty  =  empty
countstackA_out_ga(x1, x2)  =  countstackA_out_ga(x1, x2)
push(x1, x2)  =  push(x1, x2)
nil  =  nil
U1_ga(x1, x2, x3)  =  U1_ga(x1, x3)
cons(x1, x2)  =  cons(x1, x2)
U2_ga(x1, x2, x3, x4, x5)  =  U2_ga(x1, x2, x3, x5)
s(x1)  =  s(x1)
COUNTSTACKA_IN_GA(x1, x2)  =  COUNTSTACKA_IN_GA(x1)
U1_GA(x1, x2, x3)  =  U1_GA(x1, x3)
U2_GA(x1, x2, x3, x4, x5)  =  U2_GA(x1, x2, x3, x5)

We have to consider all (P,R,Pi)-chains

(4) Obligation:

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

COUNTSTACKA_IN_GA(push(nil, T35), T14) → U1_GA(T35, T14, countstackA_in_ga(T35, T14))
COUNTSTACKA_IN_GA(push(nil, T35), T14) → COUNTSTACKA_IN_GA(T35, T14)
COUNTSTACKA_IN_GA(push(cons(T79, T80), T81), s(T42)) → U2_GA(T79, T80, T81, T42, countstackA_in_ga(push(T79, push(T80, T81)), T42))
COUNTSTACKA_IN_GA(push(cons(T79, T80), T81), s(T42)) → COUNTSTACKA_IN_GA(push(T79, push(T80, T81)), T42)

The TRS R consists of the following rules:

countstackA_in_ga(empty, 0) → countstackA_out_ga(empty, 0)
countstackA_in_ga(push(nil, T35), T14) → U1_ga(T35, T14, countstackA_in_ga(T35, T14))
countstackA_in_ga(push(cons(T79, T80), T81), s(T42)) → U2_ga(T79, T80, T81, T42, countstackA_in_ga(push(T79, push(T80, T81)), T42))
U2_ga(T79, T80, T81, T42, countstackA_out_ga(push(T79, push(T80, T81)), T42)) → countstackA_out_ga(push(cons(T79, T80), T81), s(T42))
U1_ga(T35, T14, countstackA_out_ga(T35, T14)) → countstackA_out_ga(push(nil, T35), T14)

The argument filtering Pi contains the following mapping:
countstackA_in_ga(x1, x2)  =  countstackA_in_ga(x1)
empty  =  empty
countstackA_out_ga(x1, x2)  =  countstackA_out_ga(x1, x2)
push(x1, x2)  =  push(x1, x2)
nil  =  nil
U1_ga(x1, x2, x3)  =  U1_ga(x1, x3)
cons(x1, x2)  =  cons(x1, x2)
U2_ga(x1, x2, x3, x4, x5)  =  U2_ga(x1, x2, x3, x5)
s(x1)  =  s(x1)
COUNTSTACKA_IN_GA(x1, x2)  =  COUNTSTACKA_IN_GA(x1)
U1_GA(x1, x2, x3)  =  U1_GA(x1, x3)
U2_GA(x1, x2, x3, x4, x5)  =  U2_GA(x1, x2, x3, x5)

We have to consider all (P,R,Pi)-chains

(5) DependencyGraphProof (EQUIVALENT transformation)

The approximation of the Dependency Graph [LOPSTR] contains 1 SCC with 2 less nodes.

(6) Obligation:

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

COUNTSTACKA_IN_GA(push(cons(T79, T80), T81), s(T42)) → COUNTSTACKA_IN_GA(push(T79, push(T80, T81)), T42)
COUNTSTACKA_IN_GA(push(nil, T35), T14) → COUNTSTACKA_IN_GA(T35, T14)

The TRS R consists of the following rules:

countstackA_in_ga(empty, 0) → countstackA_out_ga(empty, 0)
countstackA_in_ga(push(nil, T35), T14) → U1_ga(T35, T14, countstackA_in_ga(T35, T14))
countstackA_in_ga(push(cons(T79, T80), T81), s(T42)) → U2_ga(T79, T80, T81, T42, countstackA_in_ga(push(T79, push(T80, T81)), T42))
U2_ga(T79, T80, T81, T42, countstackA_out_ga(push(T79, push(T80, T81)), T42)) → countstackA_out_ga(push(cons(T79, T80), T81), s(T42))
U1_ga(T35, T14, countstackA_out_ga(T35, T14)) → countstackA_out_ga(push(nil, T35), T14)

The argument filtering Pi contains the following mapping:
countstackA_in_ga(x1, x2)  =  countstackA_in_ga(x1)
empty  =  empty
countstackA_out_ga(x1, x2)  =  countstackA_out_ga(x1, x2)
push(x1, x2)  =  push(x1, x2)
nil  =  nil
U1_ga(x1, x2, x3)  =  U1_ga(x1, x3)
cons(x1, x2)  =  cons(x1, x2)
U2_ga(x1, x2, x3, x4, x5)  =  U2_ga(x1, x2, x3, x5)
s(x1)  =  s(x1)
COUNTSTACKA_IN_GA(x1, x2)  =  COUNTSTACKA_IN_GA(x1)

We have to consider all (P,R,Pi)-chains

(7) UsableRulesProof (EQUIVALENT transformation)

For (infinitary) constructor rewriting [LOPSTR] we can delete all non-usable rules from R.

(8) Obligation:

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

COUNTSTACKA_IN_GA(push(cons(T79, T80), T81), s(T42)) → COUNTSTACKA_IN_GA(push(T79, push(T80, T81)), T42)
COUNTSTACKA_IN_GA(push(nil, T35), T14) → COUNTSTACKA_IN_GA(T35, T14)

R is empty.
The argument filtering Pi contains the following mapping:
push(x1, x2)  =  push(x1, x2)
nil  =  nil
cons(x1, x2)  =  cons(x1, x2)
s(x1)  =  s(x1)
COUNTSTACKA_IN_GA(x1, x2)  =  COUNTSTACKA_IN_GA(x1)

We have to consider all (P,R,Pi)-chains

(9) PiDPToQDPProof (SOUND transformation)

Transforming (infinitary) constructor rewriting Pi-DP problem [LOPSTR] into ordinary QDP problem [LPAR04] by application of Pi.

(10) Obligation:

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

COUNTSTACKA_IN_GA(push(cons(T79, T80), T81)) → COUNTSTACKA_IN_GA(push(T79, push(T80, T81)))
COUNTSTACKA_IN_GA(push(nil, T35)) → COUNTSTACKA_IN_GA(T35)

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

(11) UsableRulesReductionPairsProof (EQUIVALENT transformation)

By using the usable rules with reduction pair processor [LPAR04] with a polynomial ordering [POLO], all dependency pairs and the corresponding usable rules [FROCOS05] can be oriented non-strictly. All non-usable rules are removed, and those dependency pairs and usable rules that have been oriented strictly or contain non-usable symbols in their left-hand side are removed as well.

The following dependency pairs can be deleted:

COUNTSTACKA_IN_GA(push(cons(T79, T80), T81)) → COUNTSTACKA_IN_GA(push(T79, push(T80, T81)))
COUNTSTACKA_IN_GA(push(nil, T35)) → COUNTSTACKA_IN_GA(T35)
No rules are removed from R.

Used ordering: POLO with Polynomial interpretation [POLO]:

POL(COUNTSTACKA_IN_GA(x1)) = 2·x1   
POL(cons(x1, x2)) = 2 + 2·x1 + 2·x2   
POL(nil) = 0   
POL(push(x1, x2)) = 1 + 2·x1 + x2   

(12) Obligation:

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

(13) PisEmptyProof (EQUIVALENT transformation)

The TRS P is empty. Hence, there is no (P,Q,R) chain.

(14) YES