df-nul - Metamath Proof Explorer

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Definition df-nul 3916

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 3917. (Contributed by NM, 17-Jun-1993.)

**Assertion**
Ref	Expression
df-nul	$\$

**Detailed syntax breakdown of Definition df-nul**
Step	Hyp	Ref	Expression
1		c0 3915	. 2
2		cvv 3200	. . 3
3	2, 2	cdif 3571	. 2 $\$
4	1, 3	wceq 1483	1 $\$

Colors of variables: wff setvar class

This definition is referenced by: dfnul2 3917 noel 3919

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