for F, v being LTL-formula
for s1, s2 being strict elementary LTLnode over v st s2 is_next_of s1 & F in the LTLold of s2 holds
ex L being FinSequence ex m being Nat st
( 1 <= len L & L is_Finseq_for v & L . 1 = 'X' s1 & L . (len L) = s2 & 1 <= m & m < len L & CastNode ((L . (m + 1)),v) is_succ_of CastNode ((L . m),v),F )