Add historical literature
Prove iteration lemma for S5.
Merge commit '17c29fa6d2e02a8e4617f3671ea7dfe7e16c5dca'

* commit '17c29fa6d2e02a8e4617f3671ea7dfe7e16c5dca':
  translation of GoedelGod_theorem_1_oneStep.p (THF0) into Isabelle syntax
  add file GoedelGod_consistentAssumptions.p
  corrected a typo