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Availability::- use_module(library(semweb/rdf11)).
Source[nondet]rdf_reachable(?S, +P, ?O)
[nondet]rdf_reachable(?S, +P, ?O, +MaxD, -D)
True when O can be reached from S using the transitive closure of P. The predicate uses (the internals of) rdf_has/3 and thus matches both rdfs:subPropertyOf and the inverse_of and symmetric predicate properties. The version rdf_reachable/5 maximizes the steps considered and returns the number of steps taken.

If both S and O are given, these predicates are semidet. The number of steps D is minimal because the implementation uses breadth first search.

Availability::- use_module(library(semweb/rdf_db)).
Source[nondet]rdf_reachable(?Subject, +Predicate, ?Object, +MaxD, -D)
Same as rdf_reachable/3, but in addition, MaxD limits the number of edges expanded and D is unified with the‘distance' between Subject and Object. Distance 0 means Subject and Object are the same resource. MaxD can be the constant infinite to impose no distance-limit.