1. Anand, C.K.: Harmonic morphisms of metric graphs. In: Harmonic morphisms, harmonic maps and related topics. Research Notes in Mathematics, Vol. 413. (ed. C. Anand, P. Baird, E. Loubeau, J. C. Wood), Boca Raton, FL: Chapman and Hall/CRC, 2000, pp. 97–108
2. Baird, P.: Harmonic maps with symmetry, harmonic morphisms and deformations of metrics. Research Notes in Mathematics, Vol. 87. Boston: Pitman, 1983
3. Baird, P., Eastwood, M.G.: CR geometry and conformal foliations. http://arxiv.org/abs/1011.4717v1 [math.Ds], 2010
4. Baird, P., Wehbe, M.: Shear-free ray congruences on curved space-times. http://arXiv.org/abs/0909.0241v1 [math-ph], 2009
5. Baird P., Wood J.C.: Harmonic morphisms, conformal foliations and shear-free ray congruences. Bull. Belg. Math. Soc. 5, 549–564 (1998)