// Part 2 about finding a single tour for a board+
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//================================================+
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// copy any function you need from file knight1.scala+
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type Pos = (Int, Int)    // a position on a chessboard +
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type Path = List[Pos]    // a path...a list of positions+
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//(2a) Implement a first-function that finds the first +
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// element, say x, in the list xs where f is not None. +
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// In that case return f(x), otherwise none.+
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def first(xs: List[Pos], f: Pos => Option[Path]): Option[Path] = ...+
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//(2b) Implement a function that uses the first-function for+
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// trying out onward moves, and searches recursively for an +
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// *open* tour on a dim * dim-board.+
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def first_tour(dim: Int, path: Path): Option[Path] = ...+
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