On the Zero Distribution of Solutions of Second Order Linear Differential Equations in the Complex Domain

Let f(z) 6≡ 0 be a solution of f ′′ + P (z)f = 0, where P (z) is a polynomial. Then the set of accumulation lines of zero-sequence is a subset of the Borel directions of f(z). Let f1 and f2 be two linearly independent solutions of f ′′ + P (z)f = 0, where P (z) is a polynomial of degree n and set E = f1f2. Then, for every accumulation line arg z = θ of zero-sequence of E, there is another accumulation line arg z = φ of zero-sequence of E such that |φ− θ| = 2π n+2 .