Fixed comments about [lookup].

src/BindingFormsAbs.ml

@@ -18,9 +18,9 @@ type ('bn, 'term) abs =
    define where the environment is enriched. *)
 
 (* These methods do not know the type of the environment, and do not know how
-   it is enriched or looked up; the latter task is delegated to the virtual
-   methods [extend] and [lookup]. The implementation of these methods is
-   provided by separate ``kits''. *)
+   it is enriched; the latter task is delegated to the virtual method
+   [extend]. The implementation of this method is provided by separate
+   ``kits''. *)
 
 (* We need several varieties of visitors, which is a bit painful. As of now,
    [iter], [map], [endo], [iter2] are required: see [ToolboxInput]. *)
@@ -30,9 +30,9 @@ type ('bn, 'term) abs =
    construct in a single type definition and still be able to construct
    well-typed visitors. *)
 
-(* The virtual methods [extend] and [lookup] are not polymorphic in the types
-   of bound names and environments. On the contrary, each kit comes with
-   certain specific types of bound names and environments. *)
+(* The virtual method [extend] is not polymorphic in the types of bound names
+   and environments. On the contrary, each kit comes with certain specific
+   types of bound names and environments. *)
 
 (* -------------------------------------------------------------------------- *)