@jensmaurer, @Eelis, @JohelEGP: Would you know if there's a better way to index all these cases and permutations?

Note also the index entry for "immediately-escalating function" below.

Nothing from the top of my mind.

I usually look at macros.tex to see if anything does a better job. Another method I use is looking for existing wording to see how it's done in hopes of finding a better formulation.

@tkoeppe

\defnadj{immediate-escalating}{expression}

should be your one-stop shop here.

@jensmaurer Not quite, because that also prints output, right?

Using \defnadj requires tweaking the wording. It also undoes the nesting of the adjective in the index:

One option I see is defining \indexadj, which does the indexing part of \defnadj. But that would also undo the above.