Here’s a unification failure:
The path to that is:
What I did here was feed a VP which is output of the complement extraction rule to the subject extraction rule. Of course I expected a unification failure of some kind, so it is not a problem that I have it there. What I want is to learn to analyze them better and faster.
Here’s the subject extraction rule:
basic-extracted-subj-phrase := basic-extracted-arg-phrase & head-compositional & [ SYNSEM.LOCAL.CAT.VAL [ SUBJ < >, SPR < >, COMPS < > ], HEAD-DTR.SYNSEM [ LOCAL.CAT [ VAL [ SUBJ < gap & [ LOCAL #local & local & [ CONT.HOOK.INDEX ref-ind ] ] >, COMPS olist ], MC na ], NON-LOCAL.SLASH.LIST < #local > ], C-CONT [ RELS <! !>, HCONS <! !>, ICONS <! !> ] ]. extracted-subj-phrase := basic-extracted-subj-phrase & [ SYNSEM.LOCAL.CAT.HEAD verb, HEAD-DTR.SYNSEM.LOCAL.CAT.VAL.COMPS < > ].
Is the unification failure pointing me to this line?
HEAD-DTR.SYNSEM [ LOCAL.CAT [ VAL [ SUBJ < gap & ...
Since the type gap has non-empty SLASH list:
gap := expressed-non-canonical & [ LOCAL #local, NON-LOCAL [ REL 0-dlist, QUE 0-dlist, SLASH 1-dlist & [ LIST < #local > ] ] ].
But if I look at the VP which I fed to the rule, its SUBJ’s SLASH seems is 0-1-dlist:
0-1-dlist isn’t the same as null, is it? Where did the rule get the null that it’s complaining about? Does it sound like I am not looking at the right paths after all?