Fwiffo: It is a fairly simple win. You would have needed to do two things:
Ensure the king and his fortress companions were sufficiently surrounded to stay in the fortress. This is easy.
Restrict the movement of the outer white pieces until either (a) they have no movement at all, or (b) they have to offer themselves for capture. This takes a few careful moves but is easy.
The win comes either because (A) white has no more available moves, or because (B) he has no moves except one that fatally weakens the fortress.
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