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All the articles I've read on the internet explain how a King, Knight, and Bishop should work together to defend against a King and Queen. This is called the Karstedt fortress.

This article depicts the fortress in the corner. My question is, assume the King, Knight, and Bishop are maintaining this defensive position in the middle of the board, or anywhere on the board except around the perimeter. Is there a way for the King and Queen to prevent or break down this fortress if it is not in the corner and force a win, or is this fortress strong enough to defend against a mate anywhere on the board?

If the King and Queen can force a win, how is that done?

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    note: you can investigate this sort of thing for yourself by using an online endgame tablebase
    – M.M
    Aug 23, 2016 at 22:28

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The Karstedt fortress must be set up in a corner. Even one square away it won't keep out the opposing King:

[Title "No fortress"]
[fen "6k1/5b2/7K/3nQ3/8/8/8/8 w - - 0 0"]

There is, however, a reverse fortress that keeps the stronger King imprisoned:

[Title "Draw"]
[fen "8/8/8/8/8/5nkb/2Q5/7K w - - 0 0"]

and even a mutual Zugwzang involving this configuration:

[Title "Mutual Zugzwang!"]
[fen "8/8/8/8/4k3/5n1b/8/2Q4K w - - 0 0"]

1.Qh6 Bf1!
2.Qc1 Bh3!
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