anchor.diff:        if not (Env.should_verify env)
         then U.t_true
         else (* 6 (a) *)
  -          let rec build_branch_guard scrutinee_tm pat_exp : list<typ> =
  +          let rec build_branch_guard scrutinee_tm (pattern:pat) pat_exp : list<typ> =
               let discriminate scrutinee_tm f =
                   let is_induc, datacons = Env.datacons_of_typ env (Env.typ_of_datacon env f.v) in
                   (* Why the `not is_induc`? We may be checking an exception pattern. See issue #1535. *)
  
positive.code:                   t in
  
            (* 6 (c) *)
           let branch_guard = build_and_check_branch_guard scrutinee_tm norm_pat_exp in
  
            (* 6 (d) *)
           let branch_guard =
  
negative.code: open FStar.Dyn
  open FStar.TypeChecker.Rel
  open FStar.TypeChecker.Common
  
  module S  = FStar.Syntax.Syntax
  module SS = FStar.Syntax.Subst
  module N  = FStar.TypeChecker.Normalize
  