In the Sicilian Najdorf there is a well known line which ends in threefold repition (if both players want).
[Event "NN"] [ECO "B90"] [Opening "Sicilian Defense: Najdorf Variation, English Attack, Anti- English"] [FEN ""] 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Be3 Ng4 7. Bc1 Nf6 8. Be3 Ng4
Since white retreats the bishop to c1, the positions after 5. ... a6 and 7. Bc1 are almost the same (only difference is that the knight is on g4 now) and since it is black's turn, black gained a tempo (if not for the knight's position on g4).
Two questions on this line:
- Why does black have to return the knight to f6? Aren't there any other useful moves that he could make and only retreat when being attacked?
- Ignoring any match situation or Elo difference, etc, both players insisting on this repetition, does it mean that Be3 is the best 6th move in the Najdorf for white and does it mean that normal play with 6... e5 is very dangerous for black?