 
       concat: (t) -> t.after @a
 
-      norm: -> norm @a
+      measure: -> norm @a
 
 
     # A deep finger tree.

      rest: -> new T.Digit3 @b, @c, @d
      init: -> new T.Digit3 @a, @b, @c

      norm: -> norm(@a).plus(norm(@b)).plus(norm(@c)).plus(norm(@d))


    # An empty finger tree.


      asNode: -> new T.Node2 @a, @b

      measure: -> norm @a, @b

    @Digit3 = class
      constructor: -> [@a, @b, @c] = arguments
