theorem
  H is disjunctive implies the_right_argument_of H = the_argument_of
  the_right_argument_of the_argument_of H
proof
  assume H is disjunctive;
  then H = (the_left_argument_of H) 'or' (the_right_argument_of H) by
ZF_LANG:41;
  then the_argument_of H = 'not'(the_left_argument_of H) '&' 'not' (
  the_right_argument_of H) by Th3;
  then
  the_right_argument_of the_argument_of H = 'not'(the_right_argument_of H)
  by Th4;
  hence thesis by Th3;
end;
