Certification Problem

Input (COPS 128)

We consider the TRS containing the following rules:

+(0,y) y (1)
+(x,s(y)) s(+(x,y)) (2)
+(x,y) +(y,x) (3)

The underlying signature is as follows:

{+/2, 0/0, s/1}

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:

+(x,y) +(y,x) (3)
+(x,s(y)) s(+(x,y)) (2)
+(0,y) y (1)
+(y,0) y (4)
+(s(y),x) s(+(x,y)) (5)
+(s(x32),x) s(+(x,x32)) (6)

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

1.1 Strongly closed

Confluence is proven since the TRS is strongly closed. The joins can be performed using 7 step(s).