  In this article we obtain a result about the uniqueness of factorization in
terms of conjugates of the matrix $U=(\xymatrix{1 & 1 0 & 1})$, of some
matrices representing the conjugacy classes of those elements of $SL(2,Z)$
arising as the monodromy around a singular fiber in an elliptic fibration (i.e.
those matrices that appear in Kodaira's list).
