3.1.2 Enumerating and testing objects
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Availability::- use_module(library(semweb/rdf11)).
Source[nondet]rdf_term(?Term)
True if Term appears in the RDF database. Term is either an iri, literal or blank node and may appear in any position of any triple. If Term is ground, it is pre-processed as the object argument of rdf_assert/3 and the predicate is semidet.