think about string representation.en.tex

string-representation.en.tex provides a generic string representation function that is (currently) independent of the object/problem to be represented. This needs to be provides latest in the complexity assertion explicitly. In particular this is not a definition. How do we best handle it in a modular way. I think this will also have an impact on how we refactor the complexity archive.

This also comes up when moving the problems to their "home archive" (see #5).