Fix some badly formed ontology.
Remove test for subsequent arguments to eval (for extensibility). This way, if there is a problem with the model, it is caught once at problem load time. Also remove case for null student string in match-model, in anticipation of using model as parser.
with the database.
Rename nlg-list-default -> get-default-phrase. Remove some ontology cruft.
Still need to point to them in hints and in principles tree.
Still need a way to get from principle names (which can be cryptic) to a longer explanation.
comment out debug print
and more than four matches to a student entry.
superceded. This allows student to click on "Explain more" at any time. Remove dead code for "cancelling" hint sequence.