Description: Obsolete as of 12-Aug-2023. Use alinexa or sbn instead. Lemma used in proofs of substitution properties. (Contributed by NM, 10-May-1993) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | equs3OLD | |- ( E. x ( x = y /\ ph ) <-> -. A. x ( x = y -> -. ph ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | alinexa | |- ( A. x ( x = y -> -. ph ) <-> -. E. x ( x = y /\ ph ) ) |
|
| 2 | 1 | con2bii | |- ( E. x ( x = y /\ ph ) <-> -. A. x ( x = y -> -. ph ) ) |