anchor.diff:  ///////////////////////////////////////////////////////////////////////////////
   // lib
   ///////////////////////////////////////////////////////////////////////////////
  - 
  +
  +// Test for a single TopLevelModule \in decls.  
  +let one_toplevel (decls:list<decl>) = 
  +let top,nontops = List.partition 
  +                    (fun d -> match d.d with | TopLevelModule _ -> true | _ -> false) 
  +                    decls in
  +match top with
  +| t :: [] -> Some (t,nontops)
  +| _ -> None
  +
   // We store a forest-like representation of the module namespaces for index generation.
   // SI: not used yet.
   type mforest =
  
positive.code:   | NewEffectForFree(_, RedefineEffect(i, _, _)) -> "new_effect_for_free " ^ i.idText
    | SubEffect _ -> "sub_effect"
    | Pragma _ -> "pragma"
    | Fsdoc (com,_) -> com
  
  // A decl is documented if either:
  // - it's got a fsdoc attached to it (either at top-level or in it's subtree); or
  
negative.code:     end
    | _ -> raise(FStar.Syntax.Syntax.Err("Not a TopLevelModule"))
  
  
  ///////////////////////////////////////////////////////////////////////////////
  // modul
  