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Description: The setvar x is not free in A. x e. A ph . (Contributed by NM, 18-Oct-1996) (Revised by Mario Carneiro, 7-Oct-2016)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | nfra1 |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | df-ral | ||
| 2 | nfa1 | ||
| 3 | 1 2 | nfxfr |