Angluin TODO

I still need something that evaluates an Acceptor, and returns an enumeration
the defines the language.


Language

  EnumerableLanguage

  FiniteLanguage

perhaps I should change Language to ExpressionSet, and redefine
a Language to be either finite, in which case it is defined by an ExpressionSet
or infinite, in which case it is defined by of of these AcceptorEnumeration
thingies.

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Be sure that symbols 'a' and 'a' are counted as the same, even if different
objects. (define SymbolComparator?)

Also need ExpressionComparator?

Transitions should be defined on expressions, not symbols, in order to
  be maximally general
