Certification Problem

Input (COPS 503)

We consider the TRS containing the following rules:

f(a,a,b,b) → f(c,c,c,c) (1)
a → b (2)
a → c (3)
b → a (4)
b → c (5)

The underlying signature is as follows:

{f/4, a/0, b/0, c/0}

Property / Task

Prove or disprove confluence.

Answer / Result

Yes.

Proof (by csi @ CoCo 2020)

1 Redundant Rules Transformation

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

a → c (3)
b → c (5)

All redundant rules that were added or removed can be simulated in 4 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.