def input_line_to_visible_line(self):
        """
        Return the dictionary mapping the line numbers of the input buffer to
        the lines of the screen. When a line spans several rows at the screen,
        the first row appears in the dictionary.
        """
        result = {}
        for k, v in self.visible_line_to_input_line.items():
            if v in result:
                result[v] = min(result[v], k)
            else:
                result[v] = k
        return result
Return the dictionary mapping the line numbers of the input buffer to
        the lines of the screen. When a line spans several rows at the screen,
        the first row appears in the dictionary.