Description: Reverting substitution yields the original expression. Based on fewer axioms than sbid2v , at the expense of an extra distinct variable condition. (Contributed by NM, 14-May-1993) (Revised by Wolf Lammen, 5-Aug-2023)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | sbid2vw | |- ( [ t / x ] [ x / t ] ph <-> ph ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | sbequ12r | |- ( x = t -> ( [ x / t ] ph <-> ph ) ) |
|
| 2 | 1 | sbievw | |- ( [ t / x ] [ x / t ] ph <-> ph ) |