Dutch defence
2.Bg5. This makes 2...Nf6 doubtful, since 3.Bxf6 doubles Black's pawns and makes Black's game more difficult. Black usually plays 2...g6 to fianchetto his bishop before he plays Nf6. 2...g6 marks the Leningrad variation of the Dutch defence. White's bishop cannot trapped: 2...h6 3.Bh4 g5 4.Bg3 f4? 5.e3! Mate is threatened (6.Qh5#), so the pawn on f4 is won.