anchor.diff:      weak = false;
       hnf  = false;
       primops = false;
  -    eager_unfolding = false;
  -    inlining = false;
       no_delta_steps = false;
       unfold_until = None;
       unfold_only = None;
  
positive.code:     | CheckNoUvars ->  { fs with check_no_uvars = true }
      | Unmeta ->  { fs with unmeta = true }
      | Unascribe ->  { fs with unascribe = true }
      in
      List.fold_right add_one s default_steps
  
  type psc = {
      psc_range:FStar.Range.range;
  
negative.code:     weak : bool;
      hnf  : bool;
      primops : bool;
      no_delta_steps : bool;
      unfold_until : option<S.delta_depth>;
      unfold_only : option<list<I.lid>>;
  