Remove the old function for compaction.
Compaction uses a fixpoint.
Convenience constructor for null parses.
Nullability is a property.
First order derivation tests.
Correct the indentation on commented out reduction compaction.
Omit self.
Destructuring takes a map through which it recurs.
Correct the derivative of concatenations whose first member is nullable.
Test derivatives a little further.
parseForest is a property.
Test alternation parseForest.
Test parsing the empty sequence.
Add some commented-out tests.