The Heavyside function has an awkward point:
what is the value -at- zero?
Is it 0? 1?

One way to describe it is as -both- 0 -and- 1;
you might call this:
- a multiple-valued function
- inconsistent math
- a fibre bundle (of sorts)

I'm not sure that there is a "good" answer,
but it's an amusing question.
