Description: A class is disjoint from its singleton. A consequence of regularity. (Contributed by Jonathan Ben-Naim, 3-Jun-2011) (Revised by BJ, 4-Apr-2019)
Ref | Expression | ||
---|---|---|---|
Assertion | disjcsn | |- ( A i^i { A } ) = (/) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | elirr | |- -. A e. A |
|
2 | disjsn | |- ( ( A i^i { A } ) = (/) <-> -. A e. A ) |
|
3 | 1 2 | mpbir | |- ( A i^i { A } ) = (/) |