+struct ccase;
+unsigned int interaction_case_hash (const struct interaction *, const struct ccase *, unsigned int base);
+bool interaction_case_equal (const struct interaction *, const struct ccase *, const struct ccase *);
+bool interaction_case_is_missing (const struct interaction *, const struct ccase *, enum mv_class);
+int interaction_case_cmp_3way (const struct interaction *, const struct ccase *, const struct ccase *);