e phrase.  For example, the head of an auxiliary verb phrase is
an auxiliary verb, while its semantic head is a main verb.

<p>
Predicate-argument relations of words are represented with the
attributes "mod", "arg1", ..., "arg4" in "tok".  A predicate word has
some of the above attributes, each of which represents the ID number
of an argument phrase.  In the above example, the "tok" tag for "is"
has arg1="c1" arg2="c5", and they represent the ID numbers of "Enju"
and "an efficient HPSG parser", respectively