[
=

Syntax: ($PRED <predication>)  or  [<predication>]

with: <predication> ::=
           {<compound-predication> |
           <simple-predication> |
           (match <bql-variable>
           {bab-lisp-expr. |
           <bql-variable>} |
           (element-of <bql-variable>
           {<bab-lisp-expr.> |
           <bql-variable>} |
           <lisp-type: T>}

PREDICATIONS are expressions about the knowledge
in the knowledge base. They are
characterized with brackets. A simple predication
consists of a name and one or two arguments. If the
predication has only one argument than it is
called a one-argument predication, otherwise a
two-argument predication. If predications are
combined, the resulting construct is called a
compound predication.

A ONE-ARGUMENT-PREDICATION describes a frame-instance
relation.

A TWO-ARGUMENT-PREDICATION describes a relation
between an instance and a value and is used
in connection with tell, untell and retell.

A COMPOUND-PREDICATION is a set of SIMPLE PREDICATIONs
bound with [AND, [OR or [NOT.

The expressions of the predications will be
dealt with from the left to the right.

Example: >(ask [city _city]
             (kb-format "~% ~A" _city))
         #<CAPITAL-CITY PARIS>
         #<CITY WUPPERTAL>
         #<CAPITAL-CITY LONDON>
         #<CITY DEN-HAAG>
         #<CAPITAL-CITY AMSTERDAM>
         NIL