Certification Problem

Input (COPS 82)

We consider the TRS containing the following rules:

f(a) → f(f(a)) (1)
f(x) → f(a) (2)

The underlying signature is as follows:

{f/1, a/0}

Property / Task

Prove or disprove confluence.

Answer / Result

Yes.

Proof (by csi @ CoCo 2021)

1 Redundant Rules Transformation

To prove that the TRS is (non-)confluent, we show (non-)confluence of the following modified system:

f(x) → f(a) (2)
f(a) → f(f(a)) (1)
f(x) → f(f(a)) (3)
f(a) → f(a) (4)
f(a) → f(f(f(a))) (5)

All redundant rules that were added or removed can be simulated in 2 steps .

1.1 Parallel Closed

Confluence is proven since the TRS is (almost) parallel closed. The joins can be performed using 1 parallel step(s).