  In his "Algebraic K-theory of topological spaces II" Waldhausen proved that
his functor A(X) splits: There is a canonical map from the stable homotopy of X
which has a retraction up to weak equivalence. We adapt Waldhausen's proof to
obtain a calculation of the Differential (in the sense of Goodwillie's
"Calculus I") of A(X) at any path-connected base space.
