Prove A and B are is disjoint if and only if $\sim A \cup \sim B$= the universal set.
Prove A and B are is disjoint if and only if $\sim A \cup \sim B$= the universal set.
Is this true $x \notin \left( { \sim A~ \cup \sim B} \right) \Rightarrow \quad x \in A \wedge x \in B ?$