[notdonspaulding]

> From start of game to 50 squares left is enumerable.

A nitpick, but I don't think you meant to say "enumerable" here

"enumerable" means "able to be enumerated, or counted"

https://webstersdictionary1828.com/Dictionary/Enumerate

"innumerable" means "unable to be numbered, or counted"

https://webstersdictionary1828.com/Dictionary/innumerable

[sdwr]

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 ;)