Certification Problem
Input (COPS 713)
We consider the TRS containing the following rules:
| a |
→ |
c |
(1) |
|
h(h(b,b),a) |
→ |
a |
(2) |
|
f(a) |
→ |
b |
(3) |
The underlying signature is as follows:
{a/0, c/0, h/2, b/0, f/1}Property / Task
Prove or disprove confluence.Answer / Result
No.Proof (by csi @ CoCo 2021)
1 Non-Joinable Fork
The system is not confluent due to the following forking derivations.
The two resulting terms cannot be joined for the following reason:
- When applying the cap-function on both terms (where variables may be treated like constants)
then the resulting terms do not unify.