theorem
  (CX is negation_faithful & CX is with_examples implies
  (JH,valH(Al) |= p iff CX |- p)) &
  (CX is negation_faithful & CX is with_examples implies
  (JH,valH(Al) |= q iff CX |- q)) implies
  (CX is negation_faithful & CX is with_examples
  implies (JH,valH(Al) |= p '&' q iff CX |- p '&' q)) by Th6,VALUAT_1:18;
