I'm looking for a shorter version of the noun "non-applicability" to complete the following triplet.
Truth is to true as Falsity is to false as X is to na.
What should X be?
Non-applicability has the correct meaning, but I want to find a shorter but equivalent word. For background, I'm writing a programming library and I have subprograms with names corresponding to the names of the above triplet. However, programmers hate long names so I need to find a shorter version of the last subprogram name.
Any suggestions would be appreciated.