Sun May 27 01:01:14 EDT 2018


To compute fanout, first make an iterator over all references.
A good excuse to finally understand Foldable and Traversable

Foldable is enough, likely.

Funny how implementing Foldable immedately required the generalization
to Term t, which paves the way for nested data structures, by changing
the type from 

  Term Node 

  Term (Either Node (Term Node)),