Description: Obsolete version of eqeq12 as of 23-Oct-2024. (Contributed by NM, 3-Aug-1994) (New usage is discouraged.) (Proof modification is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | eqeq12OLD | |- ( ( A = B /\ C = D ) -> ( A = C <-> B = D ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | eqeq1 | |- ( A = B -> ( A = C <-> B = C ) ) |
|
| 2 | eqeq2 | |- ( C = D -> ( B = C <-> B = D ) ) |
|
| 3 | 1 2 | sylan9bb | |- ( ( A = B /\ C = D ) -> ( A = C <-> B = D ) ) |