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|  | Predicate non_terminal/1 | 
 non_terminal :PredicateIndicator, 
...
non_terminal :PredicateIndicator, 
...non_terminal property on the predicate. This 
indicates that the predicate implements a grammar rule. See
predicate_property/2. 
The non_terminal property is set for predicates exported as Name//Arity 
as well as predicates that have at least one clause written using the
-->/2