Left Termination of the query pattern prefix_in_2(a, g) w.r.t. the given Prolog program could successfully be proven:



↳ Prolog
  ↳ PrologToPiTRSProof

Clauses:

prefix(Xs, Ys) :- app(Xs, X, Ys).
app([], X, X).
app(.(X, Xs), Ys, .(X, Zs)) :- app(Xs, Ys, Zs).

Queries:

prefix(a,g).

We use the technique of [30]. With regard to the inferred argument filtering the predicates were used in the following modes:
prefix_in: (f,b)
app_in: (f,f,b)
Transforming Prolog into the following Term Rewriting System:
Pi-finite rewrite system:
The TRS R consists of the following rules:

prefix_in_ag(Xs, Ys) → U1_ag(Xs, Ys, app_in_aag(Xs, X, Ys))
app_in_aag([], X, X) → app_out_aag([], X, X)
app_in_aag(.(X, Xs), Ys, .(X, Zs)) → U2_aag(X, Xs, Ys, Zs, app_in_aag(Xs, Ys, Zs))
U2_aag(X, Xs, Ys, Zs, app_out_aag(Xs, Ys, Zs)) → app_out_aag(.(X, Xs), Ys, .(X, Zs))
U1_ag(Xs, Ys, app_out_aag(Xs, X, Ys)) → prefix_out_ag(Xs, Ys)

The argument filtering Pi contains the following mapping:
prefix_in_ag(x1, x2)  =  prefix_in_ag(x2)
U1_ag(x1, x2, x3)  =  U1_ag(x3)
app_in_aag(x1, x2, x3)  =  app_in_aag(x3)
app_out_aag(x1, x2, x3)  =  app_out_aag(x1, x2)
.(x1, x2)  =  .(x1, x2)
U2_aag(x1, x2, x3, x4, x5)  =  U2_aag(x1, x5)
prefix_out_ag(x1, x2)  =  prefix_out_ag(x1)

Infinitary Constructor Rewriting Termination of PiTRS implies Termination of Prolog



↳ Prolog
  ↳ PrologToPiTRSProof
    ↳ PiTRS
      ↳ DependencyPairsProof

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

prefix_in_ag(Xs, Ys) → U1_ag(Xs, Ys, app_in_aag(Xs, X, Ys))
app_in_aag([], X, X) → app_out_aag([], X, X)
app_in_aag(.(X, Xs), Ys, .(X, Zs)) → U2_aag(X, Xs, Ys, Zs, app_in_aag(Xs, Ys, Zs))
U2_aag(X, Xs, Ys, Zs, app_out_aag(Xs, Ys, Zs)) → app_out_aag(.(X, Xs), Ys, .(X, Zs))
U1_ag(Xs, Ys, app_out_aag(Xs, X, Ys)) → prefix_out_ag(Xs, Ys)

The argument filtering Pi contains the following mapping:
prefix_in_ag(x1, x2)  =  prefix_in_ag(x2)
U1_ag(x1, x2, x3)  =  U1_ag(x3)
app_in_aag(x1, x2, x3)  =  app_in_aag(x3)
app_out_aag(x1, x2, x3)  =  app_out_aag(x1, x2)
.(x1, x2)  =  .(x1, x2)
U2_aag(x1, x2, x3, x4, x5)  =  U2_aag(x1, x5)
prefix_out_ag(x1, x2)  =  prefix_out_ag(x1)


Using Dependency Pairs [1,30] we result in the following initial DP problem:
Pi DP problem:
The TRS P consists of the following rules:

PREFIX_IN_AG(Xs, Ys) → U1_AG(Xs, Ys, app_in_aag(Xs, X, Ys))
PREFIX_IN_AG(Xs, Ys) → APP_IN_AAG(Xs, X, Ys)
APP_IN_AAG(.(X, Xs), Ys, .(X, Zs)) → U2_AAG(X, Xs, Ys, Zs, app_in_aag(Xs, Ys, Zs))
APP_IN_AAG(.(X, Xs), Ys, .(X, Zs)) → APP_IN_AAG(Xs, Ys, Zs)

The TRS R consists of the following rules:

prefix_in_ag(Xs, Ys) → U1_ag(Xs, Ys, app_in_aag(Xs, X, Ys))
app_in_aag([], X, X) → app_out_aag([], X, X)
app_in_aag(.(X, Xs), Ys, .(X, Zs)) → U2_aag(X, Xs, Ys, Zs, app_in_aag(Xs, Ys, Zs))
U2_aag(X, Xs, Ys, Zs, app_out_aag(Xs, Ys, Zs)) → app_out_aag(.(X, Xs), Ys, .(X, Zs))
U1_ag(Xs, Ys, app_out_aag(Xs, X, Ys)) → prefix_out_ag(Xs, Ys)

The argument filtering Pi contains the following mapping:
prefix_in_ag(x1, x2)  =  prefix_in_ag(x2)
U1_ag(x1, x2, x3)  =  U1_ag(x3)
app_in_aag(x1, x2, x3)  =  app_in_aag(x3)
app_out_aag(x1, x2, x3)  =  app_out_aag(x1, x2)
.(x1, x2)  =  .(x1, x2)
U2_aag(x1, x2, x3, x4, x5)  =  U2_aag(x1, x5)
prefix_out_ag(x1, x2)  =  prefix_out_ag(x1)
PREFIX_IN_AG(x1, x2)  =  PREFIX_IN_AG(x2)
APP_IN_AAG(x1, x2, x3)  =  APP_IN_AAG(x3)
U2_AAG(x1, x2, x3, x4, x5)  =  U2_AAG(x1, x5)
U1_AG(x1, x2, x3)  =  U1_AG(x3)

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

↳ Prolog
  ↳ PrologToPiTRSProof
    ↳ PiTRS
      ↳ DependencyPairsProof
        ↳ PiDP
          ↳ DependencyGraphProof

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

PREFIX_IN_AG(Xs, Ys) → U1_AG(Xs, Ys, app_in_aag(Xs, X, Ys))
PREFIX_IN_AG(Xs, Ys) → APP_IN_AAG(Xs, X, Ys)
APP_IN_AAG(.(X, Xs), Ys, .(X, Zs)) → U2_AAG(X, Xs, Ys, Zs, app_in_aag(Xs, Ys, Zs))
APP_IN_AAG(.(X, Xs), Ys, .(X, Zs)) → APP_IN_AAG(Xs, Ys, Zs)

The TRS R consists of the following rules:

prefix_in_ag(Xs, Ys) → U1_ag(Xs, Ys, app_in_aag(Xs, X, Ys))
app_in_aag([], X, X) → app_out_aag([], X, X)
app_in_aag(.(X, Xs), Ys, .(X, Zs)) → U2_aag(X, Xs, Ys, Zs, app_in_aag(Xs, Ys, Zs))
U2_aag(X, Xs, Ys, Zs, app_out_aag(Xs, Ys, Zs)) → app_out_aag(.(X, Xs), Ys, .(X, Zs))
U1_ag(Xs, Ys, app_out_aag(Xs, X, Ys)) → prefix_out_ag(Xs, Ys)

The argument filtering Pi contains the following mapping:
prefix_in_ag(x1, x2)  =  prefix_in_ag(x2)
U1_ag(x1, x2, x3)  =  U1_ag(x3)
app_in_aag(x1, x2, x3)  =  app_in_aag(x3)
app_out_aag(x1, x2, x3)  =  app_out_aag(x1, x2)
.(x1, x2)  =  .(x1, x2)
U2_aag(x1, x2, x3, x4, x5)  =  U2_aag(x1, x5)
prefix_out_ag(x1, x2)  =  prefix_out_ag(x1)
PREFIX_IN_AG(x1, x2)  =  PREFIX_IN_AG(x2)
APP_IN_AAG(x1, x2, x3)  =  APP_IN_AAG(x3)
U2_AAG(x1, x2, x3, x4, x5)  =  U2_AAG(x1, x5)
U1_AG(x1, x2, x3)  =  U1_AG(x3)

We have to consider all (P,R,Pi)-chains
The approximation of the Dependency Graph [30] contains 1 SCC with 3 less nodes.

↳ Prolog
  ↳ PrologToPiTRSProof
    ↳ PiTRS
      ↳ DependencyPairsProof
        ↳ PiDP
          ↳ DependencyGraphProof
            ↳ PiDP
              ↳ UsableRulesProof

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

APP_IN_AAG(.(X, Xs), Ys, .(X, Zs)) → APP_IN_AAG(Xs, Ys, Zs)

The TRS R consists of the following rules:

prefix_in_ag(Xs, Ys) → U1_ag(Xs, Ys, app_in_aag(Xs, X, Ys))
app_in_aag([], X, X) → app_out_aag([], X, X)
app_in_aag(.(X, Xs), Ys, .(X, Zs)) → U2_aag(X, Xs, Ys, Zs, app_in_aag(Xs, Ys, Zs))
U2_aag(X, Xs, Ys, Zs, app_out_aag(Xs, Ys, Zs)) → app_out_aag(.(X, Xs), Ys, .(X, Zs))
U1_ag(Xs, Ys, app_out_aag(Xs, X, Ys)) → prefix_out_ag(Xs, Ys)

The argument filtering Pi contains the following mapping:
prefix_in_ag(x1, x2)  =  prefix_in_ag(x2)
U1_ag(x1, x2, x3)  =  U1_ag(x3)
app_in_aag(x1, x2, x3)  =  app_in_aag(x3)
app_out_aag(x1, x2, x3)  =  app_out_aag(x1, x2)
.(x1, x2)  =  .(x1, x2)
U2_aag(x1, x2, x3, x4, x5)  =  U2_aag(x1, x5)
prefix_out_ag(x1, x2)  =  prefix_out_ag(x1)
APP_IN_AAG(x1, x2, x3)  =  APP_IN_AAG(x3)

We have to consider all (P,R,Pi)-chains
For (infinitary) constructor rewriting [30] we can delete all non-usable rules from R.

↳ Prolog
  ↳ PrologToPiTRSProof
    ↳ PiTRS
      ↳ DependencyPairsProof
        ↳ PiDP
          ↳ DependencyGraphProof
            ↳ PiDP
              ↳ UsableRulesProof
                ↳ PiDP
                  ↳ PiDPToQDPProof

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

APP_IN_AAG(.(X, Xs), Ys, .(X, Zs)) → APP_IN_AAG(Xs, Ys, Zs)

R is empty.
The argument filtering Pi contains the following mapping:
.(x1, x2)  =  .(x1, x2)
APP_IN_AAG(x1, x2, x3)  =  APP_IN_AAG(x3)

We have to consider all (P,R,Pi)-chains
Transforming (infinitary) constructor rewriting Pi-DP problem [30] into ordinary QDP problem [15] by application of Pi.

↳ Prolog
  ↳ PrologToPiTRSProof
    ↳ PiTRS
      ↳ DependencyPairsProof
        ↳ PiDP
          ↳ DependencyGraphProof
            ↳ PiDP
              ↳ UsableRulesProof
                ↳ PiDP
                  ↳ PiDPToQDPProof
                    ↳ QDP
                      ↳ QDPSizeChangeProof

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

APP_IN_AAG(.(X, Zs)) → APP_IN_AAG(Zs)

R is empty.
Q is empty.
We have to consider all (P,Q,R)-chains.
By using the subterm criterion [20] together with the size-change analysis [32] 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: