Negated conjunctions of conditions
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Conditions can be grouped into conjunctive sets by surrounding the set of
conditions with { and }.  The production compiler groups the test in these
conditions together.  This grouping allows for negated tests of more than one
working memory element at a time.  In the example below, the state is tested
to ensure that it does not have an object on the table.  This is equivalent
to testing: (<s> -^ontop.bottom-object.type table). If only the last
condition, (<bo> ^$type table) were negated, the production would match
against any object that was not of type table, instead of matching only when
the state has no ontop relation with a table on the bottom.

(sp blocks*negated-conjunction-example
  (goal <g> ^problem-space.name blocks-world ^state <s>)
-{(<s> ^ontop <on>)
  (<on> ^bottom-object <bo>)
  (<bo> ^type table)}
  -->
  ...
)