theorem
  H is next & H is neg-inner-most implies the_argument_of H is neg-inner-most
proof
  assume that
A1: H is next and
A2: H is neg-inner-most;
  set F = the_argument_of H;
A3: F is_subformula_of H by A1,MODELC_2:30;
  for G being LTL-formula st G is_subformula_of F holds G is negative
  implies the_argument_of G is atomic
  by A3,A2,MODELC_2:35;
  hence thesis;
end;
