TODO

Declared nat_number_of as code lemma.

For Isabelle2005:

- update course material slides to new theory headers (Tobias)

- Library/ExecutableSet.thy (Stefan)

- a global "disprove" menu item both as an action and (if it can be done)
  as a setting (Stefan & Tjark)

- convert fast_lin_arith.ML and cooper_dec.ML to use IntInf (Tobias)

- ball, bex and setsum congruence rules (Tobias & Stefan)

- remove this file (Tobias)