theorem Th66:
  r|= H1 'or' H2 iff r|= H1 or r|= H2
proof
  r|= H1 'or' H2 iff r|= Evaluate(H1,AtomicKai) 'or' Evaluate(H2,AtomicKai
  ) by Th52;
  then r|= H1 'or' H2 iff r|= Evaluate(H1,AtomicKai) or r|= Evaluate(H2,
  AtomicKai) by Th61;
  hence thesis;
end;
