theorem Th30:
  the_antecedent_of(F => G) = F & the_consequent_of(F => G) = G &
  the_argument_of F => G = F '&' 'not' G
proof
  thus the_antecedent_of(F => G) = the_left_argument_of (F '&' 'not' G) by Th1
    .= F by Th4;
  thus the_consequent_of(F => G) = the_argument_of the_right_argument_of (F
  '&' 'not' G) by Th1
    .= the_argument_of 'not' G by Th4
    .= G by Th1;
  thus thesis by Th1;
end;
