Published online by Cambridge University Press: 01 June 2009
Let ℱ be a family of meromorphic functions defined in D, all of whose zeros have multiplicity at least k+1. Let a and b be distinct finite complex numbers, and let k be a positive integer. If, for each pair of functions f and g in ℱ, f(k) and g(k) share the set S={a,b}, then ℱ is normal in D. The condition that the zeros of functions in ℱ have multiplicity at least k+1 cannot be weakened.
The research of the first author was supported by the NNSF of China (Grant No. 10771076) and the NSF of Guangdong Province, China. The research of the second author was supported by the German–Israeli Foundation for Scientific Research and Development, Grant G-809-234.6/2003.