struct ccase *datasheet_get_row (const struct datasheet *, casenumber);
bool datasheet_put_row (struct datasheet *, casenumber, struct ccase *);
bool datasheet_get_value (const struct datasheet *, casenumber, size_t column,
struct ccase *datasheet_get_row (const struct datasheet *, casenumber);
bool datasheet_put_row (struct datasheet *, casenumber, struct ccase *);
bool datasheet_get_value (const struct datasheet *, casenumber, size_t column,