theorem
  (\falseT) value_at(C,s) = FALSE
  proof
    thus (\falseT) value_at(C,s) = \not((\trueT) value_at(C,s)) by Th31
    .= 'not' ((\trueT) value_at(C,s)) by AOFA_A00:def 32 .= 'not' TRUE by Th30
    .= FALSE;
end;
