ord_symdiff/3Is true when Difference is the symmetric difference of Set1 and Set2. ord_union/2True if Union is the union of all elements in the superset SetOfSets. ord_union/3Union is the union of Set1 and Set2. ord_union/4True iff ord_union(Set1, Set2, Union) and ord_subtract(Set2, Set1, New).

F.2.32 library(persistency)

current_persistent_predicate/1	True if PI is a predicate that provides access to the persistent database DB.
db_assert/1	Assert Term into the database and record it for persistency.
db_attach/2	Use File as persistent database for the calling module.
db_attached/1	True if the context module attached to the persistent database File.
db_detach/0	Detach persistency from the calling module and delete all persistent clauses from the Prolog database.
db_retract/1