How many eastbound trains have rectangular-shaped head cars?
eastbound refers to direction = 'east'; head cars refers to position = 1
SELECT COUNT(T.train_id) FROM (SELECT T1.train_id FROM cars AS T1 INNER JOIN trains AS T2 ON T1.train_id = T2.id WHERE T1.position = 1 AND T2.direction = 'east' AND T1.shape = 'rectangle' GROUP BY T1.train_id)as T
database name:db_id trains
cars table cars Cols: id dtype integer, train id dtype integer, position dtype integer, shape dtype text, length dtype text, sides dtype text, roof dtype text, wheels dtype integer, load_shape dtype text, load number dtype integer, 
trains table trains Cols: id dtype integer, direction dtype text, 
