Theorem undm

Description: De Morgan's law for union. Theorem 5.2(13) of Stoll p. 19. (Contributed by NM, 18-Aug-2004)

	Ref	Expression
Assertion	undm	$$⊢\mathrm{V}\setminus \left(A\cup B\right)=\left(\mathrm{V}\setminus A\right)\cap \left(\mathrm{V}\setminus B\right)$$

Proof

Step	Hyp	Ref	Expression
1		difundi	$$⊢\mathrm{V}\setminus \left(A\cup B\right)=\left(\mathrm{V}\setminus A\right)\cap \left(\mathrm{V}\setminus B\right)$$