J. R. Hicks, Mr. Keynes and the "Classics"; A Suggested Interpretation, Econometrica, Vol. 5, No. 2 (Apr., 1937), pp. 147-159 ...

T. H. Gronwall, Note on the Derivatives with Respect to a Parameter of the Solutions of a System of Differential Equations, Annals of Mathematics, Vol. 20, No. 4 (Jul., 1919), pp. 292-296 ...

The article discusses a model of accent mobility and provides data to support its findings.