Copyright © 2009 Zhi-Bo Huang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
We obtain the representations of the subnormal solutions of nonhomogeneous linear
differential equation , where and are polynomials in such that and are not all constants, . We partly resolve the question raised by G. G. Gundersen and E. M. Steinbart in 1994.