Sicilian Defence, Alapin Variation

In chess, the Sicilian Defence, Alapin Variation is a response to the Sicilian Defence characterised by the moves:
It is named after the Russian master Semyon Alapin (1856–1923). For many years, it was not held in high regard, since 2...d5 was thought to allow Black easy .
Today, the Alapin is considered to be one of the most and respectable , and it is championed by grandmasters such as Evgeny Sveshnikov, Eduardas Rozentalis, Sergei Tiviakov, Duško Pavasovič, and Drazen Sermek. It has been played by World Champions Viswanathan Anand, Garry Kasparov, Anatoly Karpov, Veselin Topalov, and Vladimir Kramnik. Deep Blue played the Alapin Variation against Kasparov in their 1996 match in order to avoid a main line Sicilian that would walk into Kasparov's lifetime of experience with the opening.
The Alapin is also seen in deferred form, particularly when Black chooses an unusual second move after 2.Nf3. For example, after 2.Nf3 a6 or 2.Nf3 Qc7, 3.c3 is often seen, since neither ...a6 nor ...Qc7 are particularly useful moves against the Alapin.
Main variations.
2...Nf6.
The main line in current practice is 2... Nf6 3. e5 Nd5 and can also arise if White offers, and Black declines, the Smith–Morra Gambit (1.e4 c5 2.d4 cxd4 3.c3 Nf6 4.e5 Nd5).
White has a number of options including 4.d4, 4.Nf3, 4.g3 and 4.Bc4.
2...d5.
This is the main alternative to 2...Nf6 for Black. The usual continuation is 3. exd5 Qxd5, a line known as the Barmen Defense. 3.e5 may transpose to the Advance Variation of the French Defence if Black responds with 3...e6, but Black can also develop his c8-bishop before playing e6. This leads to a favorable version of the French for Black, since the bishop is no longer hemmed in by the pawn chain. If White plays 3.exd5, 3...Nf6 is possible, but it is not clear whether Black receives sufficient compensation for the pawn.
The main options revolve around: 
2...e6.
This is Black's most solid response, preparing 3...d5. It is closely related to the French Defence, to which it often transposes. White can transpose to the Advance Variation of the French Defence with 3.d4 d5 4.e5. Alternatively, White can transpose to a sort of Tarrasch French with 3.d4 d5 4.Nd2, or try to demonstrate a slight advantage with 3.d4 d5 4.exd5 exd5 5.Be3. 
2...d6.
This is a response. Black often offers a with 3.d4 Nf6 4.dxc5 Nc6 (4...Nxe4?? 5.Qa4+) 5.cxd6 Nxe4. White can instead play , however, with 3.d4 Nf6 4.Bd3, occupying the and maintaining a advantage.
Other tries.
2...e5.
This move makes it hard for White to play d4, but seriously weakens the d5-square. Play usually continues 3.Nf3 Nc6 4.Bc4, with a solid for White.