Coefficients associated with the expansion of certain products

Simple combinatorial interpretations are given for the coefficients of the polynomials Hn(x, y) and Gn(x, y) defined by 1l(I +Xnymt) = Gn(x, y)tn/(x)n(y)n and 11(I xnymt);l -X Hn(x, y)tn/(x)n(y) .