4...Nf6 5.f3 "An immediate transposition to the Pirc would occur. In favor of other operations, however, we must inquire into other methods of play for Black. If he continues in the style of the Pirc, merely delaying ...Nf6 for some moves the danger is that White will be able to gain a clear tempo by dispensing with f2-f3..." ---K&B
"Conclusion: ...the idea of an early ...Nc4 looks unappetising"---K&B
B)
4...a6 "A move introduced into tournament practice by Ivkov, and against an early development of the White DSB to e3 or g5 a very reasonable move too. Just as after the more common 4...c6 Black proposes to advance ...b5. The move of the a-pawn has certain advantages however: the long light diagonal is not blocked so that it may be possible to fianchetto the QB with greater effect; ...c5 is sometimes desireble in these variations and to play it after ...c6 obviously involves a loss of tempo; the knight is not deprived of the square c6. Against all this it may be objected that Black does not have any control over d5 as he does after 4...c6 and also that no avenue is opened for the deployment of the queen on the Q-side (at c7 or a5). However, such limited experience as there has been with 4...a6 has not revealed any grave defects in this move."
5...b5 6.O-O-O
6...Nd7 7.Kb1 Nb6 8.Bd3 Rb8 9.Nf3 Nc4
B1) 5.a4
B2) 5.Qd2
B3) 5.f3