Lecture given at a summerschool at Erice/Sicily, 1974 <br/><br/>
Cooperative effects  progress in synergetics 
ed. by H.Hanken 
 - Amsterdam  North-Holland Publishing Company  1974 
 - v, 301p. 
<br/><br/><label>ISBN: </label>072040309X 
<br/><br/><label>Dewey Class. No.: </label>530  / N744