le livre le plus complet et le plus instructif est celui de Viktor Moskalenko (2558)
The Budapest Defense
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You can join this group, lots of vote chess games in different lines, very instructive
http://www.chess.com/groups/home/budapest-gambiteers
I have been having trouble in my encounters with the Budapest. I know the main lines well enough, but I can't grasp the theory behind them as it is too bizarre. Can someone who knows this opening well post some of the theory behind the lines? The reason I am asking this is because even though I have acceptable knowledge of the lines, I can't punish my opponent for going out of book too early if I don't understand what's behind the moves of the opening, instead of just the moves themselves. If you post on this, thank you for your help :)