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Given the following two statements:
$$(S_1)$$ : $$(q \vee p) \to (p \leftrightarrow \sim q)$$ is a tautology
$$(S_2)$$ : $$\sim q \wedge (\sim p \leftrightarrow q)$$ is a fallacy. Then:
Let us first write clearly what every symbol means. The symbol $$\vee$$ stands for “or”, $$\wedge$$ for “and”, $$\sim$$ for “not”, $$\to$$ for “if … then …”, and $$\leftrightarrow$$ for “if and only if” (biconditional). A statement is a tautology when it is true for every possible truth-value assignment of its component variables, while it is a fallacy when it is false for every assignment.
We have two compound statements:
$$S_1 :\;(q \vee p) \to (p \leftrightarrow \sim q)$$
$$S_2 :\;\sim q \wedge (\sim p \leftrightarrow q)$$
To test whether $$S_1$$ is a tautology, we enumerate all possible truth-values of $$p$$ and $$q$$. There are four possibilities: $$(p,q) = (T,T),\,(T,F),\,(F,T),\,(F,F).$$ For every pair we shall compute each sub-expression step by step.
Case 1: $$p=T,\;q=T$$
First, $$q \vee p = T \vee T = T.$$
Next, $$\sim q = \sim T = F,$$ so $$p \leftrightarrow \sim q = T \leftrightarrow F = F$$ because a biconditional is true only when both sides have the same truth value.
Finally, $$(q \vee p) \to (p \leftrightarrow \sim q) = T \to F = F,$$ since “true implies false” is false.
Case 2: $$p=T,\;q=F$$
Here, $$q \vee p = F \vee T = T.$$
Also, $$\sim q = \sim F = T,$$ hence $$p \leftrightarrow \sim q = T \leftrightarrow T = T.$$
Thus $$(q \vee p) \to (p \leftrightarrow \sim q) = T \to T = T.$$
Case 3: $$p=F,\;q=T$$
We obtain $$q \vee p = T \vee F = T.$$
Further, $$\sim q = \sim T = F,$$ so $$p \leftrightarrow \sim q = F \leftrightarrow F = T.$$
Consequently, $$(q \vee p) \to (p \leftrightarrow \sim q) = T \to T = T.$$
Case 4: $$p=F,\;q=F$$
Now $$q \vee p = F \vee F = F.$$
Whenever the antecedent of an implication is false, the whole implication is automatically true, because $$F \to X = T$$ for any $$X$$. Therefore we do not even need to calculate the biconditional; still, for completeness we note $$\sim q = T$$ and $$p \leftrightarrow \sim q = F \leftrightarrow T = F.$$ The implication is $$F \to F = T.$$
Collecting the truth values of $$S_1$$ we have: $$F,\;T,\;T,\;T.$$ Because one row (the very first) gives false, $$S_1$$ is not a tautology. So statement $$S_1$$ is incorrect.
Next we examine $$S_2 = \sim q \wedge (\sim p \leftrightarrow q)$$ to see whether it is a fallacy. Again we test all four assignments.
Case 1: $$p=T,\;q=T$$
Compute $$\sim q = F.$$
Compute $$\sim p = F,$$ so $$\sim p \leftrightarrow q = F \leftrightarrow T = F.$$
Hence $$\sim q \wedge (\sim p \leftrightarrow q) = F \wedge F = F.$$
Case 2: $$p=T,\;q=F$$
We get $$\sim q = T.$$
Also $$\sim p = F,$$ and $$\sim p \leftrightarrow q = F \leftrightarrow F = T.$$
Therefore $$\sim q \wedge (\sim p \leftrightarrow q) = T \wedge T = T.$$ This row gives true.
Case 3: $$p=F,\;q=T$$
Here $$\sim q = F.$$
Then $$\sim p = T,$$ and $$\sim p \leftrightarrow q = T \leftrightarrow T = T.$$
Thus $$\sim q \wedge (\sim p \leftrightarrow q) = F \wedge T = F.$$
Case 4: $$p=F,\;q=F$$
Now $$\sim q = T.$$
Also $$\sim p = T,$$ giving $$\sim p \leftrightarrow q = T \leftrightarrow F = F.$$
Hence $$\sim q \wedge (\sim p \leftrightarrow q) = T \wedge F = F.$$
The truth values obtained for $$S_2$$ are $$F,\;T,\;F,\;F.$$ Because at least one row (the second) is true, the statement is not always false; therefore it is not a fallacy. Hence statement $$S_2$$ is also incorrect.
We have shown that $$S_1$$ is not a tautology and $$S_2$$ is not a fallacy. Thus both statements asserted in the question are wrong.
Hence, the correct answer is Option A.
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