Description: Sethood of certain classes. (Contributed by BJ, 2-Apr-2019)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | bj-clexab | |- ( A e. V -> { x | { x } e. ( A " B ) } e. _V ) | 
| Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | imaexg | |- ( A e. V -> ( A " B ) e. _V ) | |
| 2 | bj-snsetex |  |-  ( ( A " B ) e. _V -> { x | { x } e. ( A " B ) } e. _V ) | |
| 3 | 1 2 | syl |  |-  ( A e. V -> { x | { x } e. ( A " B ) } e. _V ) |