Description: Obsolete as of 30-Jul-2023. Use sb6 instead. (Contributed by BJ, 23-Jun-2019) (Proof shortened by Steven Nguyen, 8-Jul-2023) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | sb4vOLD | |- ( [ y / x ] ph -> A. x ( x = y -> ph ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | sb6 | |- ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) |
|
| 2 | 1 | biimpi | |- ( [ y / x ] ph -> A. x ( x = y -> ph ) ) |