[developers] [pet] unpacking

[Dan Flickinger]

Hi Sergio and Yi -

I tracked down a bug in the ERG which led to this crashing of PET for the
example you gave - in fact, also for the simpler example
     "We explained to kim why abrams arrives."
The source of the problem is that "why" is not properly constraining its
specifier (as in "exactly why") properly.  In particular (ignore the rest
of this paragraph if you don't care about the grammar-internal behavior),
the phrase "to kim" is incorrectly being allowed as a specifier, and this 
unexpected demand on "to kim" as a specifier can lead to nontermination in 
the parser, due to the analysis of non-local dependencies as in "too beautiful
to ignore" where "too" licenses a VP/NP somewhere later in the sentence,
which means it has to pass up this demand for a complement to the phrase
that "too" is a specifier for.  It is this general mechanism that passes
deferred complements up from specifier to phrase that is not yet completely
debugged, and sadly this can in principle still lead to nontermination for
certain ordinary-looking sentences.

I have corrected this flaw in the new version of the ERG which I am planning
to release tomorrow, and I'm grateful that you helped to identify such an
embarrassing black hole in the grammar before I issued the release.

Sorry to have contributed to the bewildering behavior.  Please try the new
version of the grammar once I check it in.

  Dan