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


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!




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?](https://japanese.stackexchange.com/questions/6202/is-
v-v%E3%81%AA%E3%81%84%E3%81%AB%E3%81%8B%E3%81%8B%E3%82%8F%E3%82%89%E3%81%9A-grammatical)
and <http://en.wikibooks.org/wiki/JLPT_Guide/JLPT_N2_Grammar> (search for
"にかかわらず").

