Description: Obsolete version of sb5 as of 4-Sep-2023.) (Contributed by NM, 18-Aug-1993) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | sb5OLD | |- ( [ y / x ] ph <-> E. x ( x = y /\ ph ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | sb6 | |- ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) |
|
| 2 | sb56 | |- ( E. x ( x = y /\ ph ) <-> A. x ( x = y -> ph ) ) |
|
| 3 | 1 2 | bitr4i | |- ( [ y / x ] ph <-> E. x ( x = y /\ ph ) ) |