Theorem conss1

Description: Contrapositive law for subsets. (Contributed by Andrew Salmon, 15-Jul-2011)

	Ref	Expression
Assertion	conss1	$$⊢\mathrm{V}\setminus A\subseteq B\leftrightarrow \mathrm{V}\setminus B\subseteq A$$

Proof

Step	Hyp	Ref	Expression
1		difcom	$$⊢\mathrm{V}\setminus A\subseteq B\leftrightarrow \mathrm{V}\setminus B\subseteq A$$