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