alpha beta window

[daz12]

I am a beginner and want to understand why null move uses alpha, beta=alpha+1. I am sure it's simple concept but I can't understand what difference this makes. An example would be useful!

[BrianR]

https://www.chessprogramming.org/Null_Move_Pruning

[daz12]

With null move, if there is a beta cut off, does it favour the engine and mean a normal deeper search is not required?

[BrianR]

The idea is that if the current side to move cannot improve it's score by making two moves in a row, then things must be really bad, so this line gets pruned.

Also, follow the links for the zero window bounds or search to understand the "null window" for alpha and beta.

For an example, suggest searching for Crafty source code.