Description: All setvar variables are sets (see isset ). Theorem 6.8 of Quine p. 43. (Contributed by NM, 26-May-1993) Remove use of ax-12 . (Revised by SN, 28-Aug-2023)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | vex | |- x e. _V |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | equid | |- x = x |
|
| 2 | 1 | vexw | |- x e. { x | x = x } |
| 3 | df-v | |- _V = { x | x = x } |
|
| 4 | 2 3 | eleqtrri | |- x e. _V |