anchor.diff:  //IN F*: type atom : Type0 =
   type atom = //JUST FSHARP
     | Var of var
  -  | Type of universe
  +  | Type of universe //Zoe: Not sure why this need to be an atom, just following the paper
  +  | Inductive of fv
     | Match of t * (* the scutinee *)
                (t -> t) (* the closure that pattern matches the scrutiny *) 
     | Rec of letbinding * list<t> (* Danel: This wraps a unary F* rec. def. as a thunk in F# *)
  
positive.code:     | Tm_bvar db -> //de Bruijn
        List.nth bs db.index
  
      //| Tm_fvar _ -> debug_term e; failwith "Tm_fvar: Not yet implemented"
  
      | Tm_uinst _ -> debug_term e; failwith "Tm_uinst: Not yet implemented"
  
      | Tm_type u -> mkAccTyp u
  
negative.code: let mkAccuMatch (s : t) (c : t -> t) = Accu(Match (s, c), [])
  let mkAccuRec (b:letbinding) (env:list<t>) = Accu(Rec(b, env), [])
  let mkAccTyp (u:universe) = Accu(Type u, [])
  let mkAccInd (fvar : fv) = Accu(Inductive fvar, [])
  
  let isAccu (trm:t) = 
    match trm with 
  