For all of the commands listed at the beginning of the section, we are
able to specifically exclude some collections. This is achieved by
marking a base or element name with the 
symbol as a suffix.
The usage is best illustrated by example.
Suppose, for example, that we have defined
the bases 
and 
.
Then we could define the collection E as in
That is, the base 
is defined to be 
and not 
,
where the base C is excluded.
This takes place sequentially, so that for example,
We can use this facility in conjunction with abbreviation notation as described in §6.2.2. For example,
where the constituents of C, rather than C itself, are removed.