Description: The existence of proper substitution into a class. (Contributed by NM, 7-Aug-2007) (Proof shortened by Andrew Salmon, 29-Jun-2011) (Revised by NM, 17-Aug-2018)
| Ref | Expression | ||
|---|---|---|---|
| Hypothesis | csbex.1 | |- B e. _V |
|
| Assertion | csbex | |- [_ A / x ]_ B e. _V |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | csbex.1 | |- B e. _V |
|
| 2 | csbexg | |- ( A. x B e. _V -> [_ A / x ]_ B e. _V ) |
|
| 3 | 2 1 | mpg | |- [_ A / x ]_ B e. _V |