anchor.diff:  let subst_goal subst goal =
       let g = goal.goal_ctx_uvar in
       let ctx_uvar = {
  -        g with ctx_uvar_gamma=FStar.TypeChecker.Env.rename_gamma subst g.ctx_uvar_gamma;
  +        g with ctx_uvar_gamma=Env.rename_gamma subst g.ctx_uvar_gamma;
                  ctx_uvar_typ=SS.subst subst g.ctx_uvar_typ
       } in
       { goal with goal_ctx_uvar = ctx_uvar }
  
positive.code: open FStar.All
  open FStar.Syntax.Syntax
  open FStar.TypeChecker.Env
  module Options = FStar.Options
  module SS = FStar.Syntax.Subst
  module Cfg = FStar.TypeChecker.Cfg
  
negative.code:     { g with goal_ctx_uvar = c' }
  let goal_with_env g env =
      let c = g.goal_ctx_uvar in
      let c' = {c with ctx_uvar_gamma = env.gamma ; ctx_uvar_binders = Env.all_binders env } in
      { g with goal_main_env=env; goal_ctx_uvar = c' }
  
  let mk_goal env u o b = {
  