I am having trouble understanding how "upperbound` and "lowerbound" come into play in the UCI protocol.
The spec says:
- lowerbound: the score is just a lower bound.
- upperbound: the score is just an upper bound.
For example, I see Stockfish using it like this.
info depth 22 seldepth 27 multipv 1 score cp 27 upperbound nodes 2567224
I kind of understand that it is related to the "cp." But I don't really know how. Could someone help me clarify this? It would be best if you used an example.