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 ) ) |