Question: At the 13th César Awards, a film by what director won the award for Best Film?

Context paragraphs:
4th César Awards: The 4th César Awards ceremony, presented by the Académie des Arts et Techniques du Cinéma, honoured the best French films of 1978 and took place on 3 February 1979 at the Salle Pleyel in Paris.  The ceremony was chaired by Charles Vanel and hosted by Pierre Tchernia and Jean-Claude Brialy. " L'Argent des autres" won the award for Best Film.

9 Month Stretch: 9 Month Stretch (French: 9 mois ferme ) is a 2013 French comedy film written, directed by and starring Albert Dupontel.  It was nominated for six categories at the 39th César Awards including Best Film and Best Director and Best Actor for Dupontel, winning Best Actress for its co-star Sandrine Kiberlain and Best Original Screenplay.

37th César Awards: The 37th César Awards ceremony, presented by the French Academy of Cinema Arts and Techniques (Académie des Arts et Techniques du Cinéma), was held on 24 February 2012, at the Théâtre du Châtelet in Paris.  The awards honoured the best films of 2011. " The Artist" won six out of its ten nominations, including Best Film, Best Director (Michel Hazanavicius), Best Actress (Bérénice Bejo), and Best Cinematography (Guillaume Schiffman).  The ceremony was chaired by Guillaume Canet, with Antoine de Caunes as master of ceremonies.  Nominations were announced 27 January 2012.

6th César Awards: The 6th César Awards ceremony, presented by the Académie des Arts et Techniques du Cinéma, honoured the best French films of 1980 and took place on 31 January 1981 at the Palais des Congrès in Paris.  The ceremony was chaired by Yves Montand and hosted by Pierre Tchernia. " The Last Metro" won the award for Best Film.

13th César Awards: The 13th César Awards ceremony, presented by the Académie des Arts et Techniques du Cinéma, honoured the best French films of 1987 and took place on 12 March 1988 at the Palais des Congrès in Paris.  The ceremony was chaired by Miloš Forman and hosted by Michel Drucker and Jane Birkin. " Au revoir les enfants" won the award for Best Film.

34th César Awards: The 34th César Awards ceremony was presented by the Académie des Arts et Techniques du Cinéma to honour its selection of the best films of 2008 on 27 February 2009.  Canal+ broadcast the event, which took place again at Théâtre du Châtelet in Paris, France.  The nominations for the Awards were announced on 23 January.  The ceremony was chaired by Charlotte Gainsbourg and hosted by Antoine de Caunes. " Séraphine" won the award for Best Film.

27th César Awards: The 27th César Awards ceremony, presented by the Académie des Arts et Techniques du Cinéma, honoured the best films of 2001 in France and took place on 2 March 2002 at the Théâtre du Châtelet in Paris.  The ceremony was chaired by Nathalie Baye and hosted by Édouard Baer. " Amélie" won the award for Best Film.

Au revoir les enfants: Au revoir les enfants (] , meaning "Goodbye, Children") is an autobiographical 1987 film written, produced and directed by Louis Malle.  The film won the Golden Lion at the Venice Film Festival.

Human Resources (film): Human Resources (French: Ressources humaines ) is a 1999 French-British film directed by Laurent Cantet.  As the title implies, the subject of the film is the workplace and the personal difficulties that result from conflicts among management and labour, corporations and individuals.  It stars Jalil Lespert.  Most of the other actors are non-professionals.  It won the César Award for Best First Feature Film and the César Award for Most Promising Actor at the 26th César Awards.

5th César Awards: The 5th César Awards ceremony, presented by the Académie des Arts et Techniques du Cinéma, honoured the best French films of 1979 and took place on 2 February 1980 at the Salle Pleyel in Paris.  The ceremony was chaired by Jean Marais and hosted by Pierre Tchernia and Peter Ustinov. " Tess" won the award for Best Film.

Supporting paragraphs: 13th César Awards Au revoir les enfants
Answer: Louis Malle