The research for this project was carried out while the author was at the staff of the Economics Faculty of Erasmus University Rotterdam. The core results were recorded in discussion papers 7821/G, 7901/G, 7910/G and 8002/G of the faculty''s Institute for Economic Research. Working on the project I incurred considerable debts to some professors and fellow staff members of the faculty. Professor P. J. Verdoorn initiated this study by suggesting its subject and by encouraging me to turn my initially hesitantly held view of imports as ''indispensable'' inputs into the cornerstone of the analysis; he also read the final manuscript. Professor H. C. Bos'' enthusiastic encouragement greatly stimulated me in the arduous phase of the writing of the manuscript; his advise on style and emphasis considerably improved the presentation while his careful reading of the various versions of the manuscript eliminated many non sequiturs and some errors. I am deeply in debt to A. S. W. de Vries who scrutinized not only the manuscript but also the preliminary discussion papers; while sharing an office room with him for six years I had the benefit of many stimulating discussions and he equanimously put up with my moods when I was stuck at some point. I am also in debt to D. P. Broer for checking and improving the optimal control theorem in chapter 7; to Professor R. Harkema for inducing me to write sections 5. 1 and 5.
