why () is () and [] is [] work in other way?

[Chris Angelico]

On Fri, Apr 27, 2012 at 10:07 PM, Kiuhnm
<kiuhnm03.4t.yahoo.it at mail.python.org> wrote:
> Conceptually, NaN is the class of all elements which are not numbers,
> therefore NaN = NaN. The conceptually correct way would be to check for
> 'NaN' explicitly.

Conceptually, "single-digit-numbers" is the class of all elements
which are integers [0,10). Does that mean that SdN = SdN, and
therefore that 2 = 5?

ChrisA