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 ) ) |