Et moi, ..., si. javail su comment en revenir. One service mathematics has rendered !be human race. It has put common sense back jc ny scrais point a1U: where it belongs, on the topmost sbelf next Jules Verne to be dusty canister labelled discarded non- TIle series is divergent; therefore we may be sense. able to do something with it Eric T. Bell O. Heaviside Mathematics is a tool for thought. A highly necessary tool in a world where both feedback and non- linearities abound. Similarly, all 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 bas 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 detre of this series.