code: def input_line_to_visible_line(self):
          
          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
docs: 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.