Definition df-un 3215

Description: Define the union of two classes. See elun 3221 for membership. (Contributed by SF, 10-Jan-2015.)

Assertion

Ref	Expression
df-un	|- (A u. B) = ( ∼ A &ncap ∼ B)

Detailed syntax breakdown of Definition df-un

Step	Hyp	Ref	Expression
1		cA	. . 3 class A
2		cB	. . 3 class B
3	1, 2	cun 3208	. 2 class (A u. B)
4	1	ccompl 3206	. . 3 class ∼ A
5	2	ccompl 3206	. . 3 class ∼ B
6	4, 5	cnin 3205	. 2 class ( ∼ A &ncap ∼ B)
7	3, 6	wceq 1642	1 wff (A u. B) = ( ∼ A &ncap ∼ B)

This definition is referenced by:  elun  3221  nfun  3232  symdifeq1  3249  symdifeq2  3250  dfin5  3546  uncompl  4075  unexg  4102