Hui Ling QIU, Cai Yun FANG, Ming Liang FANG
Let F be a family of meromorphic functions in a domain D, let a(z), b(z), c(z) be three distinct meromorphic functions in D, one may be ∞, and for any z∈ D, a(z)= b(z), a(z) = c(z), b(z) = c(z), and let S = {a(z), b(z), c(z)}. If for any two functions f, g∈F, f and g share the set S in D, then F is normal in D. This extends the famous Montel's criterion.