Skill is a noun, not an adjective. However in that phrase it is used as a noun adjunct, so it serves as an adjective.
Aside from that, I agree entirely. "Well, that matches my skill set" and "The two jobs need completely different skill sets" being valid singular and plural uses, respectively.
Edit 2
After your edit, the question becomes one of whether a group of things can be taken as a collective singular, such as in this question, which asks such things as whether a dozen somethings “is” enough.
The answer is that it can be singular if you are thinking of it as one thing as a whole, just as in:
Twelve miles is much too far for me to walk before lunch.
In that sort of sentence, you get agreement like this:
- A few more games is all I have time for.
- A handful of games is all I have time for.
- A few more miles is all I have time for.
- A handful of miles is all I have time for.
It really just depends on what you’re trying to say, and how you’re trying to say it. If you want to say that five matches is more than you can handle or that three olives is too many for a martini, then yes, sure you can.
But normally plural things take plural agreement — see the ngram below, which shows that a handful of men will usually take plural agreement because men is plural, no matter the status of the a handful of premodifer.
It is only when you logically group them as one thing that they take singular agreement. By doing so, that is what you are conveying.
But perhaps your friend does not like it when the council is decided on something, as opposed to when they are divided. :)
Original Answer
Your friend is right, and you are wrong.
When you have a premodifier like a lot of, a number of, or a handful of preceding the head noun, the verb continues to agree with that head noun, instead of with the notionally singular a lot, a number, a handful, which functions more like a red herring than anything else.
Ok, seriously, these premodifiers are really acting like adjectives, not like prepositional phrases. That means the head noun remains the head noun, and there is no change to agreement:
- People think the same way.
- Several people think the same way.
- Few people think the same way.
- No people think the same way.
- Many people think the same way.
- A lot of people think the same way.
- A number of people think the same way.
- A handful of people think the same way.
As opposed to something like:
- If just one out of all those people thinks the same way as you do, you win.
Edit
Although there is a bit of room for variation here, depending on just what the writer is thinking, there is a clear dominance of the plural continuing to be used after a handful of men in this Google N-Gram chart:
Best Answer
It should be "combine with the default set A or B" in this example. If you were to have options where each choice is a set of sets, then "the default sets" would be correct. In quick, relaxed English speech, this rule may not be followed. For example, with your second sentence, any person directing crowds toward queues may say "join queues A or B," but it would be better to say "join queue A or B" as in "join the queue labeled A or the queue labeled B." I would not use "join the queue A or B," so there is some irregularity here.
A set is a singular entity, no matter how many elements it has, so the singular would be best, complete with a definite article for clarity. English speakers are used to phrases such as "combine with defaults sets A or B" in everyday speech and so this would probably remain unnoticed, even in a paper. I am almost certain both examples have been used in professional settings (not that that forbids a correct answer, but if there is an incorrect one, it is quite forgivable).
I hope this was of some help!
Edit: There is a sort of interesting thing about the word "or" in that in English, as in most other languages, it is inclusive. That is, it could also mean "and" if written without any additional quantifiers. If that is the case (if one does not forbid exclusivity), the "and" implies a multiple and would change "set" to "sets." Perhaps this contradicts the earlier parts of my answer, but it is an important nuance that comes from additional thinking on it.
So, when you say "[It] earns exactly one of the adjudications respectively of Tables 3, 4, 5 or 6." that "exactly one" is very important. This, to me, forbids the "and," thus I believe "Table" would be best. However, many English speakers may not be used to this, having the inclusive "or" on the mind at most times, and may even find it a bit unnatural to see "Table" instead of "Tables" even in this context.