Description: Reversal of substitution. (Contributed by AV, 6-Aug-2023)
Ref | Expression | ||
---|---|---|---|
Assertion | sbbibvv | |- ( A. y ( [ y / x ] ph <-> ps ) <-> A. x ( ph <-> [ x / y ] ps ) ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | nfv | |- F/ y ph |
|
2 | nfv | |- F/ x ps |
|
3 | 1 2 | sbbib | |- ( A. y ( [ y / x ] ph <-> ps ) <-> A. x ( ph <-> [ x / y ] ps ) ) |