theorem Th65:
  r|= H1 '&' H2 iff r|= H1 & r|= H2
proof
  r|= H1 '&' H2 iff r|= Evaluate(H1,AtomicKai) '&' Evaluate(H2,AtomicKai)
  by Th51;
  then
  r|= H1 '&' H2 iff r|= Evaluate(H1,AtomicKai) & r|= Evaluate(H2,AtomicKai
  ) by Th58;
  hence thesis;
end;
