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Mirrors > Home > MPE Home > Th. List > df-nul | Unicode version |
Description: Define the empty set. Special case of Exercise 4.10(o) of [Mendelson] p. 231. For a more traditional definition, but requiring a dummy variable, see dfnul2 3786. (Contributed by NM, 17-Jun-1993.) |
Ref | Expression |
---|---|
df-nul |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | c0 3784 | . 2 | |
2 | cvv 3109 | . . 3 | |
3 | 2, 2 | cdif 3472 | . 2 |
4 | 1, 3 | wceq 1395 | 1 |
Colors of variables: wff setvar class |
This definition is referenced by: dfnul2 3786 noel 3788 |
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