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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_to_recent(self, notebook):

 """
 Add an entry to recent notebooks.
 
 We only maintain the list of the 20 most recent notebooks.
 """

        if notebook not in self.recent_notebooks:
            self.recent_notebooks.insert(0, notebook)
            self.recent_notebooks = self.recent_notebooks[:20]