theorem exeqi {x: nat} (a b: wff x): $ a <-> b $ > $ E. x a <-> E. x b $;
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | exeq | A. x (a <-> b) -> (E. x a <-> E. x b) |
|
| 2 | hyp h | a <-> b |
|
| 3 | 2 | ax_gen | A. x (a <-> b) |
| 4 | 1, 3 | ax_mp | E. x a <-> E. x b |