## Thinking Mathematically (6th Edition)

The negation of $p\rightarrow q$ is $p\land \sim q$. De Morgan's Laws says that $\sim (p\land q)\equiv \sim p\lor \sim q$ and $\sim (p\lor q)\equiv \sim p\land \sim q$. Thus here the negation is: $p\land \sim(\sim r\lor s)\equiv p\land ( r \land \sim s)$