+ - get rid of Sequence.Singleton if possible
+
+ - use 'a'-'z' or 'a-z' instead of [a-z]?
+ - de-genericize?
+ - foo.add(x)
+ foo.add(y.andnot(x)) ==> this is broken
+ - distinguish Conjunct from Sequence?
+ => !(Conjunct instanceof Reducible)
+ - avoid building the parts of the tree that end up getting dropped
+ - is it worth adding an additional class of states for these?
+ - or perhaps just a runtime node marker (hasNonDroppedParent)
+ - "ambiguity modulo dropped fragments"?
+ - this may conceal highly inefficient grammars...
+ - double-check all the region logic
+ - automatically collect time statistics and display
+
+______________________________________________________________________________
+v1.1
+
+ - MUST HAVE BETTER ERROR MESSAGES
+ - use for developing java15.g
+ - better ambiguity reporting
+ - colorized tree-diffs?
+ - graphviz?
+ - better toString() methods all around...
+
+ - Treewalker code compiler?
+ - detect and reject circular gramars
+ - skeleton generator?
+ - precedes restrictions ("<-")
+ - More topology untangling [later]
+ - grammar highlighting?
+ - Forest needs a "manual access" API (lifting makes this hard)
+ - rewriting language? multiple passes?