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BI
BI is used to connect forms of the verb "be" to some idiomatic
expressions. Forms of "be" therefore have BI+, directly
disjoined with their other connectors:

	are: Sp- & (Pg+ or Pv+ or Pp+ or .... or BI+)

Some title words like "chairman", "president", "head", etc., can
serve as complements of "be" without taking an article. For such
words, special dictionary entries have been created:

	president.i chairman.i: {@AN-} & BI-;

Indirect questions can act as complements of "be" as well, but
only when the subject of "be" is a word like "question":

	       +-Ss*q+BIq+
               |     |   |    		       
	The question is who killed Nicole
       *The murderer is who killed Nicole

The S connectors on words like "question" are thus given a
special "Ss*q" subscript. Question words are given a BIq-
connector. Post-processing then dictates that these BIq
connectors cannot be used unless a Ss#q is present in the
group. Question words have BIq- directly disjoined with QI-
and W- connectors, used in direct and indirect questions.

The phrase "because (clause)" can be a complement with "be" as
well, but only if the subject is "this" or "that". "This" and
"that" are thus given Ss*b+; "because" is given BIh-; and
post-processing dictates that a BIh requires a Ss#b. (These
words are also among the subjects that can take "(be)
(indirect question)" as a predicate; Ss#b is thus added to
Ss#q in post-processing as a connector that permits BIq.)

Grammar Documentation Page.