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2. J. Cerf: Thesis, Paris.
3. The diffeomorphism group of a compact Riemann surface;Earle;Bull. Am. math. Soc.,1967
4. Curves on 2-manifolds and isotopies;Epstein;Acta Math.,1966
5. The fundamental group of a surface and a theorem of Schreier;Griffiths;Acta Math.,1963