theorem
  (\falseT) value_at(C,u) = FALSE
  proof
    thus (\falseT) value_at(C,u) = \not((\trueT) value_at(C,u)) by Th47
    .= 'not' ((\trueT) value_at(C,u)) by AOFA_A00:def 32 .= 'not' TRUE by Th46
    .= FALSE;
  end;
