anchor.diff:  delete(Cache2, N, X, APageId, A = #page{p0 = AP0, e = AE}) ->
     ?dbg("delete(~p, ~p)~n", [X, A]),
     case binsearch(AE, X) of
  -    {not_found, R} ->
  +    ?not_found(R) ->
         QPageId =
           if R =:= 0 -> AP0;
              true -> item_p(element(R, AE))
  
positive.code:         {Cache3, false} ->
            {Cache3, false}
        end;
      {found, K} ->
        %% found, now delete a^.e[k]
        R = K - 1,
        QPageId =
  
negative.code: %%%_* Binary search within a page ==============================================
  %%%
  %%% Search a page's item vector E for key X.
  %%% Return ?found(K) if found at index K, otherwise ?not_found(R) where R is the
  %%% index where the B-tree traversal should descend.
  %%% Callers MUST match on ?not_found(R) before matching on ?found(K).
  
  -define(not_found(R), {not_found, R}).
  -define(found(K), {found, K}).
  
  binsearch(E, X) ->
    binsearch(E, X, 1, size(E)).
  