less brutal Metis failure -- the brutality was accidentally introduced by df8ae0590be2
session Sequents = Pure +
  description {*
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1991  University of Cambridge
    Classical Sequent Calculus based on Pure Isabelle.
  *}
  options [document = false]
  theories
    LK
    ILL
    ILL_predlog
    Washing
    Modal0
    T
    S4
    S43
session "Sequents-LK" in LK = Sequents +
  description {*
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1992  University of Cambridge
    Examples for Classical Logic.
  *}
  options [document = false]
  theories
    Propositional
    Quantifiers
    Hard_Quantifiers
    Nat