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Question 67

Consider the following two propositions :
$$P_1:\sim(p\to\sim q)$$

$$P_2:(p\land\sim q)\land(\sim p\lor q)$$
If the proposition $$p\to(\sim p\lor q) $$ is evaluated as FALSE, then

For an implication

$$A\to B$$

to be FALSE,

$$A=\text{TRUE},\qquad B=\text{FALSE}$$

Hence,

$$p=\text{TRUE}$$

and

$$\sim p\lor q=\text{FALSE}$$

Now, an OR statement is FALSE only when both parts are FALSE.

Therefore,

$$\sim p=\text{FALSE},\qquad q=\text{FALSE}$$

Thus,

$$p=\text{TRUE},\qquad q=\text{FALSE}$$

Now,

$$P_1=\sim(p\to\sim q)$$

Since

$$p=\text{TRUE},\qquad \sim q=\text{TRUE}$$

we get

$$p\to\sim q=\text{TRUE}$$

Hence,

$$P_1=\sim(\text{TRUE})=\text{FALSE}$$

Also,

$$P_2=(p\land\sim q)\land(\sim p\lor q)$$

$$=(\text{TRUE}\land\text{TRUE})\land(\text{FALSE}\lor\text{FALSE})$$

$$=\text{TRUE}\land\text{FALSE}$$

$$=\text{FALSE}$$

Therefore, both $$P_1$$ and $$P_2$$ are FALSE.

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