Disjunctions of constants
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If a set of constants are contained within double angle brackets (i.e., {<<}
and >>), the condition will match a working memory element that has any one
of those constants.  Variables cannot occur within a disjunction.  There must
be spaces separating the brackets from the constants.  For instance, in the
previous example, the state's color attribute must have blue or red as the
value for the production to match.

Legal disjunctions    Illegal disjunctions 
{<< A B C 45 I17 >>}    {<< <A> A >>}  
{<< good-morning good-evening >>}   {<<A B C >>}