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;
reserve L,L9 for FinSequence;

theorem Th28:
  H is_immediate_constituent_of F implies len H < len F
proof
  assume
A1: H is_immediate_constituent_of F;
  per cases by A1;
  suppose
A2: F is negative or F is next;
    then H = the_argument_of F by A1,Th20,Th21;
    hence thesis by A2,Th10;
  end;
  suppose
A3: F is conjunctive or F is disjunctive or F is Until or F is Release;
    then H = the_left_argument_of F or H = the_right_argument_of F by A1,Th22
,Th23,Th24,Th25;
    hence thesis by A3,Th11;
  end;
end;
