Enumerable as in "computationally enumerable", or "able to be enumerated in a reasonable amount of time x cpu x memory" The beginning and end of the game have

Enumerable as in "computationally enumerable", or "able to be enumerated in a reasonable amount of time x cpu x memory" The beginning and end of the game have less possibilities to consider. The midgame has the most possible moves = hardest to calculate. If you read carefully, the midgame is the bit the author avoids explaining how to solve ;)