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[Dean Hickerson]

Mostly to Jonathan Post:

> Trapped on a holiday morning with no PC or even hand calculator about, I
> started enumerating by hand the nonisomorphic partial endofunctions on n
> indistinguishable objects.

I haven't seen the word "endofunction" before.  Do you just mean a function
from some subset of the set of n elements into the same set of n elements?

> That is, charted by digraphs with outdegree 0 or 2 at each vertex.

Do you mean "outdegree 0 or 1"?

> There are 5 PFGs on 2 points: 0 arcs and 0, 1, or 2 loops on two
> disconnected vertices, and 1->2 where 2 either has no out-link or a loop.

If I understand correctly what you're counting, I find 6 of them; with
1->2, 2 can either have no out-link, or a loop, or an arc back to 1.

Am I confused about what you're counting, or did you miss one?

Dean Hickerson
dean at math.ucdavis.edu