reserve k,n,m for Nat,
  a,x,X,Y for set,
  D,D1,D2,S for non empty set,
  p,q for FinSequence of NAT;
reserve F,F1,G,G1,H,H1,H2 for LTL-formula;
reserve sq,sq9 for FinSequence;

theorem Th23:
  F is disjunctive 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 disjunctive;
  then F = (the_left_argument_of F) 'or' (the_right_argument_of F) by Th7;
  hence thesis by Th16;
end;
