> I’m convinced that there’s a proper mathy / lighting-y word for each component in that expression.

Sometimes yes, but often no. Frequently this kind of expression is the result of solving an equation, so it’s just an expression.

Graphics people often use two approaches for sub-expressions:

- You can name them with the same letters that are in the expression, just with the punctuation & operators removed, for example:

    const uvMinusNTimesDt = uv.sub(n.mul(dt))

- Alternatively, just like with equations, math people often freely assign single letter names to variables without worrying about semantic meaning.

    const q = uv.sub(n.mul(dt))

Nothing really wrong with naming sub-expressions after fruits, or single letters, or spelling them out explicitly.

It might be worth reflecting on what the goals are with your naming, and whether it matters what they’re named. As software engineers, our biases lean toward making choices that improve readability and maintainability. But for a specific equation that will never change once it works correctly, our preconceived notions about good software design and best practices might not actually apply to this situation. It might be more important to document the source of the equation than to make the implementation readable.