anchor.diff:                  | UnivArgs _::_ ->
                     failwith "Ill-typed term: universes cannot be applied to term abstraction"
   
  -               | Match _::_ -> 
  +                | Match _::_ -> 
                     failwith "Ill-typed term: cannot pattern match an abstraction"
   
                   | Arg(c, _, _)::stack -> 
  
positive.code:                  let stack = us::stack in
                   norm cfg env stack t'
       
            | Tm_name x -> 
              rebuild cfg env stack t
             
            | Tm_fvar f -> 
              let should_delta = match cfg.delta_level with 
                  | NoDelta -> false
  
negative.code:   | UnfoldUntil of S.delta_depth
    | Beta            
    | BetaUVars
    | Simplify        //Simplifies some basic logical tautologies: not part of definitional equality!
    | EraseUniverses
    | AllowUnboundUniverses //we erase universes as we encode to SMT; so, sometimes when printing, it's ok to have some unbound universe variables
    //remove the rest?
  