What's the meaning of しない as in …するしない？

Question

My textbook contains the following sentence

参加するしないにかかわらず、必ず返事を葉書で出してください。
(Regardless of whether you participate or not, kindly make sure to RSVP by postcard.)

as an example of the expression 名詞＋にかかわらず. While I get the whole sentence and the にかかわらず, I'm having trouble understanding this usage of しない. I know しない

• as the ない形 of する
• as in 市内 (within the city)
• as in 竹刀 (bamboo sword)

but none of these three seem to make sense, and the first one isn't even a 名詞.

Could someone please explain しない in this context and the general pattern of how/when to use it?

Thanks!

Answer 1

It's the negative of する、しない. The point missing in the textbook is that this pattern is either 'noun + にかかわらず' or 'verb + opposite verb + にかかわらず', e.g.

• するしないにかかわらず
• 来る来ないにかかわらず
• etc.

See also Is "V Vないにかかわらず" grammatical? and http://en.wikibooks.org/wiki/JLPT_Guide/JLPT_N2_Grammar (search for "にかかわらず").

Answer 2

This しない is simply the negative of する; "don't do". The 参加するしない part of the sentence means, regardless (～にかかわらず) of if you participate (参加する) or if you don't participate (参加しない).

With this form for "regardless of" (～にかかわらず; also could be ～を問わず), if often takes contrasting or "opposite" ideas. So the 参加するしない is a compact way to list the two choices of participating or not. I think it would also be grammatically correct to say 参加するかしないかにかからわず, but I'm not 100% certain on that.