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Published online by Cambridge University Press: 14 August 2015
The subject allotted to me in the program is the ‘Summary of Symposia I–III: problems considered and present status of them’. Perhaps I should have been more cautious when I agreed to this title about two years ago. For it means that, if I do my job well, you will know the present status of all problems and the Symposium is finished today. However, I am sure that, no matter how I try, there will remain enough for other speakers and for other days of discussion. For this reason, in surveying the field, I shall not consciously try to avoid the topics of other speakers. Overlap will do no harm.