The classical problem of finding conditions on the entire coefficients A(z)A(z) and B(z)B(z) guaranteeing that all nontrivial solutions of f′′+A(z)f′+B(z)f=0f″+A(z)f′+B(z)f=0 are of infinite order is discussed. Some such conditions which involve deficient value, Borel exceptional value and extremal functions for Denjoy's conjecture are obtained.
