1.d4 d5 2.e4 e5

White can play: 3.exd5 and the best reply for black is 3...f6 (3...b5 4.h3 or 4.d5; 3...Nh6 4.Bxh6; 3...Bb4 4.c3).

Other moves: 3.Nf3 and 3.Bh6 Nxh6.

If 3.dxe5 then 3...Bc5 4.Be3 Qh4 5.g3 dxe4 6.Qd4 Qe7 and black wins.