Unifies Term with the most general instance of the dynamic clause or recorded term indicated by the database reference Ref.
db_reference, must be nonvar
Ref must be instantiated to a database
reference to an existing clause or recorded term.
not sensitive to the source module and can be used to access any
clause, regardless of its module.
if Ref is not instantiated
if Ref is not a syntactically valid database reference
if Ref is a syntactically valid database reference but does not refer to an existing clause or recorded term.
| ?- assert(foo:bar,R). R = '$ref'(771292,1) | ?- instance('$ref'(771292,1),T). T = (bar:-true) | ?- clause(H,B,'$ref'(771292,1)). no | ?- clause(foo:H,B,'$ref'(771292,1)). H = bar, B = true