let v be LTL-formula; :: thesis: for N being strict LTLnode over v
for w being Element of Inf_seq AtomicFamily
for U being Choice_Function of (BOOL (Subformulae v)) st not N is elementary & chosen_formula (U,N) is Until & w |= the_right_argument_of (chosen_formula (U,N)) holds
( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) )

let N be strict LTLnode over v; :: thesis: for w being Element of Inf_seq AtomicFamily
for U being Choice_Function of (BOOL (Subformulae v)) st not N is elementary & chosen_formula (U,N) is Until & w |= the_right_argument_of (chosen_formula (U,N)) holds
( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) )

let w be Element of Inf_seq AtomicFamily; :: thesis: for U being Choice_Function of (BOOL (Subformulae v)) st not N is elementary & chosen_formula (U,N) is Until & w |= the_right_argument_of (chosen_formula (U,N)) holds
( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) )

let U be Choice_Function of (BOOL (Subformulae v)); :: thesis: ( not N is elementary & chosen_formula (U,N) is Until & w |= the_right_argument_of (chosen_formula (U,N)) implies ( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) ) )
set SN = chosen_succ (w,v,U,N);
set H = chosen_formula (U,N);
set H2 = the_right_argument_of (chosen_formula (U,N));
set SNO = the LTLold of (chosen_succ (w,v,U,N));
set SNN = the LTLnew of (chosen_succ (w,v,U,N));
set NO = the LTLold of N;
set NN = the LTLnew of N;
assume not N is elementary ; :: thesis: ( not chosen_formula (U,N) is Until or not w |= the_right_argument_of (chosen_formula (U,N)) or ( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) ) )
then A1: chosen_formula (U,N) in the LTLnew of N by Th58;
( chosen_formula (U,N) is Until & w |= the_right_argument_of (chosen_formula (U,N)) implies ( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) ) )
proof
assume that
A2: chosen_formula (U,N) is Until and
A3: w |= the_right_argument_of (chosen_formula (U,N)) ; :: thesis: ( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) )
A4: chosen_succ (w,v,U,N) = SuccNode2 ((chosen_formula (U,N)),N) by A2, A3, Def35;
LTLNew2 (chosen_formula (U,N)) = {(the_right_argument_of (chosen_formula (U,N)))} by A2, Def2;
then A5: the LTLnew of (chosen_succ (w,v,U,N)) = ( the LTLnew of N \ {(chosen_formula (U,N))}) \/ ({(the_right_argument_of (chosen_formula (U,N)))} \ the LTLold of N) by A1, A4, Def5;
A6: now :: thesis: ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N )end;
A8: chosen_formula (U,N) in {(chosen_formula (U,N))} by TARSKI:def 1;
the LTLold of (chosen_succ (w,v,U,N)) = the LTLold of N \/ {(chosen_formula (U,N))} by A1, A4, Def5;
hence ( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) ) by A8, A6, XBOOLE_0:def 3; :: thesis: verum
end;
hence ( not chosen_formula (U,N) is Until or not w |= the_right_argument_of (chosen_formula (U,N)) or ( ( the_right_argument_of (chosen_formula (U,N)) in the LTLnew of (chosen_succ (w,v,U,N)) or the_right_argument_of (chosen_formula (U,N)) in the LTLold of N ) & chosen_formula (U,N) in the LTLold of (chosen_succ (w,v,U,N)) ) ) ; :: thesis: verum