+struct casereader;
+struct dictionary;
+struct variable;
+
+struct sort_criteria *sort_parse_criteria (const struct dictionary *,
+ struct variable ***, int *,
+ bool *saw_direction);
+void sort_destroy_criteria (struct sort_criteria *);
+
+struct casefile *sort_execute (struct casereader *,
+ const struct sort_criteria *);
+int sort_active_file_in_place (const struct sort_criteria *);
+struct casefile *sort_active_file_to_casefile (const struct sort_criteria *);