def make_board(N):
    """
    Utility function that returns a new N x N empty board (empty spaces represented by '*')
    Arg N: integer - board dimensions - must be greater than or equal to 1
    """
    assert N >= 1, "Invalid board dimension";
    assert type(N) == int, "N must be an integer";
    return [["*" for x in range(N)] for x in range(N)];