'Move the cursor up one line in the same column. If the cursor
is at the first line, create a new line at the top.'

def reverse_index(self):

    (top, bottom) = self.margins
    if (self.cursor.y == top):
        self.buffer.pop(bottom)
        self.buffer.insert(top, take(self.columns, self.default_line))
    else:
        self.cursor_up()
