6.2. Pointers to Stacks

I wanted to add support for such games as Der Katzenschwanz and Die Schlange in which stacks could be initialized to several dozens of cards.
That made stacks way too long and caused every board to consume a lot of memory.
Solution: keep one copy of each stack once in a dynamically allocated memory.
Each state contains an array of pointers to each of its stacks.
That made it possible to scale up to a million states and more.