Certification Problem

Input (TPDB SRS_Standard/Waldmann_19/random-158)

The rewrite relation of the following TRS is considered.

a(a(a(a(x1)))) → a(b(a(b(x1)))) (1)
a(a(b(a(x1)))) → a(b(a(a(x1)))) (2)
b(a(b(b(x1)))) → b(b(a(a(x1)))) (3)

Property / Task

Prove or disprove termination.

Answer / Result

Yes.

Proof (by AProVE @ termCOMP 2023)

1 Semantic Labeling

Root-labeling is applied.

We obtain the labeled TRS
aa(aa(aa(aa(x1)))) → ab(ba(ab(ba(x1)))) (4)
aa(aa(aa(ab(x1)))) → ab(ba(ab(bb(x1)))) (5)
aa(ab(ba(aa(x1)))) → ab(ba(aa(aa(x1)))) (6)
aa(ab(ba(ab(x1)))) → ab(ba(aa(ab(x1)))) (7)
ba(ab(bb(ba(x1)))) → bb(ba(aa(aa(x1)))) (8)
ba(ab(bb(bb(x1)))) → bb(ba(aa(ab(x1)))) (9)

1.1 Dependency Pair Transformation

The following set of initial dependency pairs has been identified.
aa#(aa(aa(aa(x1)))) → ba#(ab(ba(x1))) (10)
aa#(aa(aa(aa(x1)))) → ba#(x1) (11)
aa#(aa(aa(ab(x1)))) → ba#(ab(bb(x1))) (12)
aa#(ab(ba(aa(x1)))) → ba#(aa(aa(x1))) (13)
aa#(ab(ba(aa(x1)))) → aa#(aa(x1)) (14)
aa#(ab(ba(ab(x1)))) → ba#(aa(ab(x1))) (15)
aa#(ab(ba(ab(x1)))) → aa#(ab(x1)) (16)
ba#(ab(bb(ba(x1)))) → ba#(aa(aa(x1))) (17)
ba#(ab(bb(ba(x1)))) → aa#(aa(x1)) (18)
ba#(ab(bb(ba(x1)))) → aa#(x1) (19)
ba#(ab(bb(bb(x1)))) → ba#(aa(ab(x1))) (20)
ba#(ab(bb(bb(x1)))) → aa#(ab(x1)) (21)

1.1.1 Reduction Pair Processor

Using the linear polynomial interpretation over the naturals
[aa#(x1)] = 1 · x1
[aa(x1)] = 1 + 1 · x1
[ba#(x1)] = 1 + 1 · x1
[ab(x1)] = 1 + 1 · x1
[ba(x1)] = 1 + 1 · x1
[bb(x1)] = 1 + 1 · x1
the pairs
aa#(aa(aa(aa(x1)))) → ba#(x1) (11)
aa#(ab(ba(aa(x1)))) → aa#(aa(x1)) (14)
aa#(ab(ba(ab(x1)))) → aa#(ab(x1)) (16)
ba#(ab(bb(ba(x1)))) → ba#(aa(aa(x1))) (17)
ba#(ab(bb(ba(x1)))) → aa#(aa(x1)) (18)
ba#(ab(bb(ba(x1)))) → aa#(x1) (19)
ba#(ab(bb(bb(x1)))) → ba#(aa(ab(x1))) (20)
ba#(ab(bb(bb(x1)))) → aa#(ab(x1)) (21)
could be deleted.

1.1.1.1 Dependency Graph Processor

The dependency pairs are split into 0 components.