1.Nf3 f6 2.d4

Black can play 2...d5. Possible lines:

3.Ne5 Bg4 4.f3 fxe5 5.fxg4,

3.g3 Bg4 4.Bh3 Nh6 5.0-0,

3.e4 Nh6 4.Bh6 Bg4 5.exd5 g6,

3.Nc3 c6 (or 3...b5, 3...a6),

3.Na3 b5 4.g3 Nh6 (or 4...Bh3, 4...Bg4) 6.Bxh6 or 5.Ne5,

3.c4.

2...e6 is playable.