[E-Lang] Immutable map operations

[Tyler Close]

Dean wrote:
> BTW The PartiallyComparable comment says that MarkM "discovered"
> irreflexive partial ordering.  Seems like the concept was around
> before.  Does it really come from him?

I'd never come across the concept before. I got the impression that
MarkM hadn't seen it before either. If you have a better reference for
this idea, please tell me and I will update the documentation. In the
Hydro documentation, I've made an attempt to include references to
what I think are the sources of the concepts I've used in the design.

Tyler