theorem Th25:
  F is Release implies (H is_immediate_constituent_of F iff H =
  the_left_argument_of F or H = the_right_argument_of F)
proof
  assume F is Release;
  then F = (the_left_argument_of F) 'R' (the_right_argument_of F) by Th9;
  hence thesis by Th18;
end;
