1.Nf3 f6 2.e3 e6 3.Nd4 c6 4.Nb5

Black's main line is now 4...cxb5.

Another possible move is 4...Bd6 but white will end better.

If 4...Qa5 then 5.b4 (5.N1c3) Qa4 (5...Nh6) 6.Qh5 (or 6.Qg4 Bd6 7.Nc7 Kd8 and white is winning) g6 7.Qxh7 and white should win.

If 4...Bb4 then 5.N1c3 and 5...Bxc3 6.Nc7; 5...cxb5 6.Nb5; black should prefer 5...Nh6 or 5...g6; white can also play 5.c3.