Certification Problem

Input (TPDB TRS_Standard/SK90/2.24)

The rewrite relation of the following TRS is considered.

fib(0) → 0 (1)
fib(s(0)) → s(0) (2)
fib(s(s(x))) → +(fib(s(x)),fib(x)) (3)

Property / Task

Prove or disprove termination.

Answer / Result

Yes.

Proof (by ttt2 @ termCOMP 2023)

1 Rule Removal

Using the linear polynomial interpretation over (3 x 3)-matrices with strict dimension 1 over the naturals
[fib(x1)] =
1 0 0
0 0 1
0 0 1
· x1 +
1 0 0
0 0 0
0 0 0
[+(x1, x2)] =
1 1 0
0 1 0
0 0 0
· x1 +
1 0 1
0 0 0
0 0 0
· x2 +
0 0 0
0 0 0
0 0 0
[0] =
0 0 0
0 0 0
0 0 0
[s(x1)] =
1 1 1
1 0 1
0 0 1
· x1 +
1 0 0
0 0 0
0 0 0
all of the following rules can be deleted.
fib(0) → 0 (1)
fib(s(0)) → s(0) (2)

1.1 Rule Removal

Using the linear polynomial interpretation over (3 x 3)-matrices with strict dimension 1 over the naturals
[fib(x1)] =
1 1 0
0 1 1
0 1 1
· x1 +
0 0 0
0 0 0
0 0 0
[+(x1, x2)] =
1 0 0
0 0 0
0 1 0
· x1 +
1 0 0
0 0 0
1 0 0
· x2 +
0 0 0
0 0 0
0 0 0
[s(x1)] =
1 0 0
1 1 1
0 1 0
· x1 +
1 0 0
0 0 0
0 0 0
all of the following rules can be deleted.
fib(s(s(x))) → +(fib(s(x)),fib(x)) (3)

1.1.1 R is empty

There are no rules in the TRS. Hence, it is terminating.