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 Th9:
  H is Release implies H = (the_left_argument_of H) 'R' (
  the_right_argument_of H)
proof
  assume
A1: H is Release;
  then
A2: not H is Until by Lm21;
A3: ( not H is conjunctive)& not H is disjunctive by A1,Lm21;
  then ex H1 st H = H1 'R' the_right_argument_of H by A1,A2,Def20;
  hence thesis by A1,A3,A2,Def19;
end;
