One service mathematics has rendered the 'Ht moi, ...* Ii j'avait so comment en revenir, je ny _ais point aile':' human race. It has put common sense back Jules Verne where it belongs, on the topmost shelf neJll to the dusty canister labelled 'discarded non- The series is diwrgent; therefore we may be sense' . * ble to do something with it. Eric T. Bell O. H eniside Mathematics is a tool for thought. A highly necessary tool in a world where both feedback and non- linearities abound. Similarly, alI kinds of parts of mathematics serve as tools for other parts and for other sciences. Applying a simple rewriting rule to the quote on the right above one finds such statements as: 'One service topology has rendered mathematical physics ...'; 'One service logic has rendered com- puter science ...'; 'One service category theory has rendered mathematics ...'. All arguably true. And all statements obtainable this way form part of the raison d't!tre of this series.