const struct ccase *lagged_case (const struct dataset *ds, int n_before);
void dataset_need_lag (struct dataset *ds, int n_before);
void dataset_set_callback (struct dataset *ds, void (*cb) (void *), void *);
const struct ccase *lagged_case (const struct dataset *ds, int n_before);
void dataset_need_lag (struct dataset *ds, int n_before);
void dataset_set_callback (struct dataset *ds, void (*cb) (void *), void *);