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Predicate safe_meta/2
 sandbox:safe_meta(+Goal, -Called) is semidet[multifile, library(aggregate)]
Declare the aggregate meta-calls safe. This cannot be proven due to the manipulations of the argument Goal.
 safe_meta(+Goal, -Called:list(callable)) is semidet[multifile, library(sandbox)]
Hook. True if Goal is a meta-predicate that is considered safe iff all elements in Called are safe.
 sandbox:safe_meta(+Goal, -Called) is semidet[multifile, library(pengines_sandbox)]
Declare the pengine meta-predicates as safe. Note that the pengine calling predicates are safe because the safety is guaranteed by the recieving pengine.