Certification Problem

Input (TPDB SRS_Standard/Secret_06_SRS/multum6)

The rewrite relation of the following TRS is considered.

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

Property / Task

Prove or disprove termination.

Answer / Result

Yes.

Proof (by AProVE @ termCOMP 2023)

1 String Reversal

Since only unary symbols occur, one can reverse all terms and obtains the TRS
b(c(c(x1))) → b(c(a(x1))) (5)
a(b(c(a(x1)))) → c(c(b(x1))) (6)
c(a(b(x1))) → a(c(b(a(x1)))) (7)
a(c(b(x1))) → b(a(c(x1))) (8)

1.1 Dependency Pair Transformation

The following set of initial dependency pairs has been identified.
b#(c(c(x1))) → b#(c(a(x1))) (9)
b#(c(c(x1))) → c#(a(x1)) (10)
b#(c(c(x1))) → a#(x1) (11)
a#(b(c(a(x1)))) → c#(c(b(x1))) (12)
a#(b(c(a(x1)))) → c#(b(x1)) (13)
a#(b(c(a(x1)))) → b#(x1) (14)
c#(a(b(x1))) → a#(c(b(a(x1)))) (15)
c#(a(b(x1))) → c#(b(a(x1))) (16)
c#(a(b(x1))) → b#(a(x1)) (17)
c#(a(b(x1))) → a#(x1) (18)
a#(c(b(x1))) → b#(a(c(x1))) (19)
a#(c(b(x1))) → a#(c(x1)) (20)
a#(c(b(x1))) → c#(x1) (21)

1.1.1 Reduction Pair Processor

Using the linear polynomial interpretation over the naturals
[b#(x1)] = 1 · x1
[c(x1)] = 1 · x1
[a(x1)] = 1 · x1
[c#(x1)] = 1 · x1
[a#(x1)] = 1 · x1
[b(x1)] = 1 + 1 · x1
the pairs
a#(b(c(a(x1)))) → b#(x1) (14)
c#(a(b(x1))) → b#(a(x1)) (17)
c#(a(b(x1))) → a#(x1) (18)
a#(c(b(x1))) → b#(a(c(x1))) (19)
a#(c(b(x1))) → a#(c(x1)) (20)
a#(c(b(x1))) → c#(x1) (21)
could be deleted.

1.1.1.1 Dependency Graph Processor

The dependency pairs are split into 2 components.