NaN in Lua 5.3 Reference Manual

["John Hind" <john.hind@...>]

Enrique Garcia Cota said:
<<
Wouldn't this be enough?

    function isNan(x)
      return x ~= x
    end

Or if you want something a bit more resistant against tables with 
metatable magic:

    function isNan(x)
      return type(x) == 'number' and x ~= x
    end
>>

Oh, that is so cleaver! I should know better than to suggest something 
is impossible on this mailing list!

However depending on NaN being the *only* value that is not equal to 
itself arguably fails my stipulation of robustness, and intuitive it 
ain't! Is 'minus infinity' equal to itself? Is 'minus infinity' equal to 
'plus infinity' even? (remembering we we not relying on IEEE 
conformance). I think we enter deep philosophical waters!