Chess Opening Theory/1. e4/1...c5/2. Nf3/2...d6/3. d4/3...cxd4/4. Qxd4

White recaptures on d4 with their queen. This is an irregular continuation that avoids the main line Open Sicilians.

Usually it is considered unprincipled to develop one's queen early because it can be a target affording the enemy valuable tempo. However, here White argues that their queen is hard for Black to exploit because they have played ...d6.

After 4...Nc6, attacking the queen, White pins and trades off the knight with 5. Bb5 Bd7 6. Bxc6. Then, the usual continuation is 6...Bxc6 7. Nc3 Nf6 8. Bg5 e6 9. O-O-O Be7 10. Rhe1 O-O.

4...a6 prepares ...Nc6 to gain time on the queen by cutting out the response Bb5. One line is 5. c4 Nc6 6. Qd2; another line is to trade the queens off with 5. Be3 Nc6 6. Qb6 Qxb6 7. Bxb6.

The earliest recorded appearance of this opening was in the third unofficial chess Olympiad, in Munich in 1936.^[1]

Vitaly Chekhover (1908―1965) was a Soviet chess player from St. Petersburg, who played this variation in 1938.^[2]

1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Qxd4

Wikipedia has related information at Sicilian Defence, Chekhover Variation.