void interaction_destroy (struct interaction *);
void interaction_add_variable (struct interaction *, const struct variable *);
void interaction_dump (const struct interaction *);
void interaction_to_string (const struct interaction *iact, struct string *str);
void interaction_destroy (struct interaction *);
void interaction_add_variable (struct interaction *, const struct variable *);
void interaction_dump (const struct interaction *);
void interaction_to_string (const struct interaction *iact, struct string *str);