1. P. Di Francesco, P. Mathieu and D. Sénéchal, Conformal Field Theory, Graduate Texts in Contemporary Physics, springer (1996).
2. V.G. Knizhnik, A.M. Polyakov and A.B. Zamolodchikov, Mod. Phys. Lett. A3:819 (1988). J. Distler and H. Kawai, Nucl. Phys. B321:509 (1989) F. David, Mod. Phys. Lett. A3:1651 (1988)
3. W. Tutte, A Census of Planar Maps, Canad. Jour. of Math. 15:249–271 (1963) A Census of planar triangulations, Canad. Jour. of Math. 14:21–38 (1962) A Census of Hamiltonian polygons, Canad. Jour. of Math. 14:402417 (1962)
4. G. 't Hooft, Nucl. Phys. B72:461 (1974).
5. E. Brézin C. Itzykson, G. Parisi and J.-B. Zuber, Planar Diagrams, Comm. Math. Phys. 59:35–51 (1978).