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We know that we have distributive rules that handle the disjunction and the conjunction, such as the following

    \begin{align*} p \and (q \orr r) &\Leftrightarrow (p \and q) \orr (p \and r)\\ p \orr (q \and r) &\Leftrightarrow (p \orr q) \and (p \orr r). \end{align*}

But, does there exist a rule, for example, that would handle distributivity of the conjunction with the implication? In other words,

    \[\text{is } p \and (q \rightarrow r) \text{ logically equivalent to } (p \and q) \rightarrow (p \and r)?\]

At least, the above case, the answer is no. We can see this by constructing a truth table like the one below; the truth values of p \and (q \rightarrow r) are not the same as (p \and q) \rightarrow (p \and r).  Hence, p \and (q \rightarrow r) and (p \and q) \rightarrow (p \and r) are not logically equivalent. Therefore, it’s not a rule that we can apply in our proofs.

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So begins another school year, and the Basic Discrete Mathematics course is in full swing. This Monty Python clip is almost mandatory viewing for a logic course. It’s a twist on the classic comedic sketch: a man walks into a shop and wants something strange—this time it’s an argument.

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