Certification Problem

Input (COPS 671)

We consider the TRS containing the following rules:

f(f(f(b))) → b (1)
h(h(a,a),h(f(f(a)),h(c,b))) → f(c) (2)

The underlying signature is as follows:

{f/1, b/0, h/2, a/0, c/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:

h(h(a,a),h(f(f(a)),h(c,b))) → f(c) (2)
f(f(f(b))) → b (1)

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

1.1 Critical Pair Closing System

Confluence is proven using the following terminating critical-pair-closing-system R:

There are no rules.

1.1.1 R is empty

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