anchor.diff:  %%   elements to be built in memory at one time.
   %%
   %% - iterator_from(K, B): returns an iterator that can be used for
  -%%   traversing the entries of B-tree / B*-tree B with key greater 
  +%%   traversing the entries of B-tree / B*-tree B with key greater
   %%   than or equal to K; see `next'.
   %%
   %% - keys(B): returns an ordered list of all keys in B-tree / B*-tree B.
   %%
  -%% - largest(B): returns {K, V}, where K is the largest key in 
  -%%   B-tree / B*-tree B, and V is the value associated with K in B. 
  +%% - largest(B): returns {K, V}, where K is the largest key in
  +%%   B-tree / B*-tree B, and V is the value associated with K in B.
   %%   Assumes that the B-tree / B*-tree B is nonempty.
   %%
  -%% - lookup(K, B): looks up key K in B-tree / B*-tree B; returns {value, V}, 
  +%% - lookup(K, B): looks up key K in B-tree / B*-tree B; returns {value, V},
   %%   or `none' if the key K is not present.
   %%
   %% - map(F, B): maps the function F(K, V) -> V' to all key-value pairs
  -%%   of the B-tree / B*-tree B and returns a new B-tree / B*-tree B' 
  +%%   of the B-tree / B*-tree B and returns a new B-tree / B*-tree B'
   %%   with the same set of keys as B and the new set of values V'.
   %%
   %% - next(I): returns {K, V, I1} where K is the smallest key referred to
  
positive.code: %% -----------------------------------------------------------------------------
  %% Operations:
  %%
  %% - empty(O): returns empty B-tree of order O. Order is defined as 
  %%   the maximum number of children nodes a non-leaf node may hold.
  %%   The minimum value is 4.
  %%
  %% - empty(O, b_star): returns empty B*-tree of order O. Order is 
  %%   defined as the maximum number of children nodes a non-leaf node 
  %%   may hold. The minimum value is 4.
  %%
  %% - enter(K, V, B): inserts key K with value V into B-tree / B*-tree B 
  %%   if the key is not present in the tree, otherwise updates key K to 
  %%   value V in B. Returns the new tree.
  %%
  %% - from_dict(O, L): turns a list L of {Key, Value} pairs into
  
negative.code: 
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  %% Data structure:
  %% - {BTreeType, Minimum, Maximum, NumberKeyValues, Tree},
  %%   where `Tree' is composed of :
  %%   - {KeyNo, IsLeaf, [{Key, Value}], [Tree]}.
  
  