def make_move(self, x, y):
if self.board[y][x] == '<STR_LIT:U+0020>':<EOL><INDENT>return lens.board[y][x].set(self.player)(self)<EOL><DEDENT>return self<EOL>
Return a board with a cell filled in by the current player. If
        the cell is already occupied then return the board unchanged.