Construct a Sudoku Game Object
an n^2 x n^2 matrix object to represent the game
Other additional arguments (currently ignored)
Coerce an object to one that can be used as a sudoku game. IMPORTANT: games are represented as n^2xn^2 character matrices, using 1-9 for n=2 or 3, and LETTERS[1:(n^2)] for n = 4 or 5.
An object of class 'sudoku'
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