Editing Petrov's Defence (section)

====3...d6====
Most often, White follows the main line 3...d6 4.Nf3 Nxe4 5.d4 (5.Bd3{{chesspunc|!?}} is also playable, known as the Millennium Attack) d5 6.Bd3. This position is similar to an [[French Defence#Exchange Variation: 3.exd5|Exchange French]] in which Black has played the extra move ...Nf6-e4, however this extra move is not necessarily to Black's advantage. White will try to drive Black's advanced knight from e4 with moves like c4 and Re1. In practice White is usually able to achieve this, but at some structural cost such as having to play c4, which balances out.<ref name="Burgess">{{Citation |last=Burgess |first=Graham |author-link=Graham Burgess |title=The Mammoth Book of Chess |year=2010 |publisher=Running Press }}</ref> White can also force simplification with [[Emanuel Lasker|Lasker]]'s 5.Qe2 Qe7 6.d3.  This is generally only good enough for a [[draw (chess)|draw]], which Black should be satisfied with.  Another possibility, explored by [[Paul Keres|Keres]], is 5.c4, known as the Kauffmann Attack.

A completely different approach is to meet 4...Nxe4 with 5.Nc3 Nxc3 6.dxc3 with rapid {{chessgloss|development}} and {{chessgloss|queenside}} [[castling]]. For instance, White can plan a quick Be3, Qd2, and 0-0-0, and play for a {{chessgloss|kingside}} attack, trusting that his [[doubled pawns|doubled]] c-pawns will help protect his king, and that his [[Initiative (chess)|initiative]] and attacking potential will offset the longterm disadvantage of having doubled pawns. In the 5.Nc3 line, Black must avoid 5...Bf5{{chesspunc|??}} 6.Qe2! which wins a piece due to the [[pin (chess)|pin]] (if 6...Qe7 7.Nd5, forcing 7...Qd7 because of the threat to the c7-pawn; then 8.d3 wins the piece). [[Viswanathan Anand]] resigned after only six moves after falling for this against [[Alonso Zapata]] at Biel in 1988.<ref>{{cite web |url=http://www.chessgames.com/perl/chessgame?gid=1018015 |title=Alonso Zapata vs. Viswanathan Anand |website=[[ChessGames.com]] |access-date=13 June 2011 }}</ref>

The Cochrane Gambit, 4.Nxf7, is labelled "speculative but entertaining" by [[Nick de Firmian]] in ''[[Modern Chess Openings]]'' (''MCO'') 14th edition. He evaluates the position in [[Veselin Topalov]]–[[Vladimir Kramnik]], [[Linares chess tournament|Linares 1999]] as offering chances for both sides after 4...Kxf7 5.Nc3 c5!? 6.Bc4+ Be6 7.Bxe6+ Kxe6 8.d4 Kf7 9.dxc5 Nc6.<ref>{{citation |last=de Firmian |first=Nick |author-link=Nick de Firmian |title=[[Modern Chess Openings]] |edition=14th |year=1999 |publisher=Random House |isbn=0-8129-3084-3}}</ref>  

The Paulsen Variation, 4.Nc4, is labelled "ineffective" by de Firmian in ''MCO'', but is occasionally seen at grandmaster level. US master Andrew Karklins has experimented with 4.Nd3!?, now called the Karklins–Martinovsky Variation. This was played in the [[World Chess Championship 2018]] between [[Magnus Carlsen]] and [[Fabiano Caruana]].<ref>{{cite web |url=https://www.chessgames.com/perl/chessgame?gid=1937789 |title=Magnus Carlsen vs. Fabiano Caruana, 2018 |website=[[Chessgames.com]] }}</ref>