Description: If a formula holds for some value of a variable not occurring in it, then it holds for all values of that variable. (Contributed by BJ, 28-Dec-2020)
Ref | Expression | ||
---|---|---|---|
Assertion | ax5ea | |- ( E. x ph -> A. x ph ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ax5e | |- ( E. x ph -> ph ) |
|
2 | ax-5 | |- ( ph -> A. x ph ) |
|
3 | 1 2 | syl | |- ( E. x ph -> A. x ph ) |