### Database Schema:
CREATE TABLE trains (
	id	INTEGER	NOT NULL	PRIMARY KEY,
	direction	TEXT	NULL	DEFAULT NULL
);

CREATE TABLE cars (
	id	INTEGER	NOT NULL	PRIMARY KEY,
	train_id	INTEGER	NULL	DEFAULT NULL,
	position	INTEGER	NULL	DEFAULT NULL,
	shape	TEXT	NULL	DEFAULT NULL,
	len	TEXT	NULL	DEFAULT NULL,
	sides	TEXT	NULL	DEFAULT NULL,
	roof	TEXT	NULL	DEFAULT NULL,
	wheels	INTEGER	NULL	DEFAULT NULL,
	load_shape	TEXT	NULL	DEFAULT NULL,
	load_num	INTEGER	NULL	DEFAULT NULL,
	foreign key (train_id) references trains (id)
);

### User's Query:
Please list the IDs of all the trains that run in the east direction and have less than 4 cars.

### Extra Knowledge:
less than 4 cars refers to carsNum < 4
SELECT T1.id FROM trains AS T1 INNER JOIN ( SELECT train_id, MAX(position) AS carsNum FROM cars GROUP BY train_id ) AS T2 ON T1.id = T2.train_id WHERE T1.direction = 'east' AND T2.carsNum < 4