“The head-template followed by the ellipsis http://docs.racket-lang.org/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29\|... indicate that the elements of the constructed lists are created from 0 or more head templates.” Is it “indicate” or “indicates”?

Or syndicate?

(i would guess indicates, but one also says “there are no issues”, i.e., plural with 0 elements. English is hard.)

Apropos of nothing - Syndicate was a pretty neat Amiga game.

I would say “indicates” is correct, because the text refers specifically to the combination of the head-template and the ellipsis. It’s kinda like they’re fused into the one symbol, and thus the singular form would be appropriate. But yeah, English is a… um, I can’t think of the appropriate word to describe how daft I find English to be (as a native speaker who has tried a tiny bit to learn some other languages).

The phrase “followed by the ellipsis …” modifies “head-template,” so in this sentence, the head-template is the subject that’s doing the indicating, and the verb should agree with it (“the head-template … indicates”). But in terms of the meaning of the sentence, I’m not sure that’s quite right; I think a better correction would be something that joins two subjects together with “and,” like “The head-template and the ellipsis following it indicate […].”

“The combination of the head-template and the ellipsis following it indicates […]” would work too, because then the subject is “combination”