Jens update

This is mostly German so I add @heiland as a reviewer. @chellappa, you can wait for his approval.

For

Differentialgleichung it is probably debatable if it should be included. Currently, I think most, standard dicts support both this and the recommended (by Duden) Differenzialgleichung, I hardly know anyone in Math who would like that recommendation a lot though. So, as we probably keep using the "t" writing in our texts it might be good to make sure we have it in. @all opinions?