# Predicate Logic and Popular Culture (Part 84): OMD

Let $F(s,t)$ be the proposition “You said at time $s$ that we’d still be friends at time $t$.” Translate the logical statement

$\forall s<0 \exists t>0 F(s,t)$.

This matches the last line of the first chorus from “If You Leave.”

For what it’s worth, this was the opening song on the Pretty in Pink soundtrack, which remains for my money the best movie soundtrack ever made.

Context: This semester, I taught discrete mathematics for the first time. Part of the discrete mathematics course includes an introduction to predicate and propositional logic for our math majors. As you can probably guess from their names, students tend to think these concepts are dry and uninteresting even though they’re very important for their development as math majors.

In an effort to making these topics more appealing, I spent a few days mining the depths of popular culture in a (likely futile) attempt to make these ideas more interesting to my students. In this series, I’d like to share what I found. Naturally, the sources that I found have varying levels of complexity, which is appropriate for students who are first learning prepositional and predicate logic.

When I actually presented these in class, I either presented the logical statement and had my class guess the statement in actual English, or I gave my students the famous quote and them translate it into predicate logic. However, for the purposes of this series, I’ll just present the statement in predicate logic first.

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