[developers] LKB vs. PET divergences

[Ann Copestake]

looking at the grammar now ...

oe at csli.Stanford.EDU said:
> looking at the definition of the rule, i also noticed it uses multiple
> supertypes in the instance definition.  this is generally illegal, but
> happens to succeed in this case, because for:

>   vstem-vstem-rule := head-final-type & orth-princ & [...]

> there appears to be a glb in the type hierarchy.  both systems seem to
> compile the above without complaint, but i believe the above situation
> should be flagged or outright rejected as syntactically ill-formed.

No, it's not illegal.  The stuff on the RHS of the := is just a definition of 
a TFS and so there's no formal reason to require that just one type should be 
specified.  It's valid to have no types or many types there.  If there isn't a 
type which is the glb of the types specified, the description will fail to 
unify and will thus fail.

It is an unclear definition, however, and someone might want to write a 
checker to make sure that definitions meet various conventions, but I don't 
think such a check should be built into the AVM reading code or made part of 
the syntax.

Ann