*** Guide-to-Links ***
CX is used in comparative constructions like the following:

		           |      |
	He has more money than I do

Normally an auxiliary like "do" or "have" must be followed by
a participle. In cases like the above, however, this need can
be satisfied by a preceding comparative word like "as" or
"than". Auxiliaries thus carry

        do: S- & (I+ or CX-...) 

See "MV: Comparatives V".

CX is also used in a few cases of nouns that take relative
clauses consisting only of auxiliaries, like "everything".

 +-Sp*i+---Os---+      +-Sp*i+
 |     |        |      |     |
I.p read.v everything I.p could.v 

With a cost of 2, we allow auxiliaries to be used without any
participle or complement, under any circumstances. Thus "I do"
and "I could" are accepted.

Grammar Documentation Page.