1. L. V. Ahlfors and L. Sario, Riemann
surfaces, Princeton Univ. Press, Princeton, N. J. (1960).
2. C. K. Anand, Harmonic morphisms of metric graphs, In `Harmonic morphisms, harmonic maps, and related topics’ (eds.: C. K. Anand, P. Baird, E. Loubeau, and J. C. Wood), Research Notes in Mathematics Vol. 413, Chapman & Hall (1999), 109–112.
3. M. T. Anderson, Complete minimal varieties in hyperbolic space, Inventiones Math. 69 (1982), 477–494.
4. J. Barta, Sur la vibration fundamentale d’une membrane, C. R. Acad. Sci. 204 (1937), 472–473.
5. I. Benjamini and O. Schramm, Random walks and harmonic functions on infinite planar graphs using square tilings, Annals of Probability 24 (1996), 1219–1238.