+double interaction_value_get_nonzero_entry (const struct interaction_value *);
+const union value *interaction_value_get (const struct interaction_value *);
+const struct variable * interaction_variable_get_var (const struct interaction_variable *);
+size_t interaction_get_n_numeric (const struct interaction_variable *);
+size_t interaction_get_n_alpha (const struct interaction_variable *);
+size_t interaction_get_n_vars (const struct interaction_variable *);
+const struct variable * interaction_variable_get_member (const struct interaction_variable *, size_t);
+bool is_interaction (const struct variable *, const struct interaction_variable **, size_t);
+struct interaction_value *
+interaction_case_data (const struct ccase *, const struct variable *,
+ const struct interaction_variable **, size_t);
+double interaction_value_get_nonzero_entry (const struct interaction_value *);