Certification Problem

Input (TPDB SRS_Standard/Trafo_06/un07)

The rewrite relation of the following TRS is considered.

b(b(x1)) → b(a(b(x1))) (1)
b(b(a(b(x1)))) → b(a(b(a(a(b(b(x1))))))) (2)
b(a(b(x1))) → b(a(a(b(x1)))) (3)
b(a(a(b(a(b(x1)))))) → b(b(x1)) (4)

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
bb(bb(x1)) → ba(ab(bb(x1))) (5)
bb(ba(x1)) → ba(ab(ba(x1))) (6)
bb(ba(ab(bb(x1)))) → ba(ab(ba(aa(ab(bb(bb(x1))))))) (7)
bb(ba(ab(ba(x1)))) → ba(ab(ba(aa(ab(bb(ba(x1))))))) (8)
ba(ab(bb(x1))) → ba(aa(ab(bb(x1)))) (9)
ba(ab(ba(x1))) → ba(aa(ab(ba(x1)))) (10)
ba(aa(ab(ba(ab(bb(x1)))))) → bb(bb(x1)) (11)
ba(aa(ab(ba(ab(ba(x1)))))) → bb(ba(x1)) (12)

1.1 Dependency Pair Transformation

The following set of initial dependency pairs has been identified.
bb#(bb(x1)) → ba#(ab(bb(x1))) (13)
bb#(ba(x1)) → ba#(ab(ba(x1))) (14)
bb#(ba(ab(bb(x1)))) → ba#(ab(ba(aa(ab(bb(bb(x1))))))) (15)
bb#(ba(ab(bb(x1)))) → ba#(aa(ab(bb(bb(x1))))) (16)
bb#(ba(ab(bb(x1)))) → bb#(bb(x1)) (17)
bb#(ba(ab(ba(x1)))) → ba#(ab(ba(aa(ab(bb(ba(x1))))))) (18)
bb#(ba(ab(ba(x1)))) → ba#(aa(ab(bb(ba(x1))))) (19)
bb#(ba(ab(ba(x1)))) → bb#(ba(x1)) (20)
ba#(ab(bb(x1))) → ba#(aa(ab(bb(x1)))) (21)
ba#(ab(ba(x1))) → ba#(aa(ab(ba(x1)))) (22)
ba#(aa(ab(ba(ab(bb(x1)))))) → bb#(bb(x1)) (23)
ba#(aa(ab(ba(ab(ba(x1)))))) → bb#(ba(x1)) (24)

1.1.1 Reduction Pair Processor

Using the linear polynomial interpretation over the naturals
[bb#(x1)] = 2 + 2 · x1
[ba#(x1)] = -2 + 2 · x1
[ab(x1)] = 2 + x1
[ba(x1)] = x1
[bb(x1)] = 2 + x1
[aa(x1)] = -2 + x1
the pairs
bb#(ba(ab(bb(x1)))) → ba#(aa(ab(bb(bb(x1))))) (16)
bb#(ba(ab(bb(x1)))) → bb#(bb(x1)) (17)
bb#(ba(ab(ba(x1)))) → ba#(aa(ab(bb(ba(x1))))) (19)
bb#(ba(ab(ba(x1)))) → bb#(ba(x1)) (20)
ba#(ab(bb(x1))) → ba#(aa(ab(bb(x1)))) (21)
ba#(ab(ba(x1))) → ba#(aa(ab(ba(x1)))) (22)
could be deleted.

1.1.1.1 Dependency Graph Processor

The dependency pairs are split into 0 components.