anchor.diff:  
   -export([check/2, print/2]). % for debugging only
   
  +-export_type([btree/1]).
  +
   %%%_* Types and macros =========================================================
   
   %-define(DEBUG, true).
  
positive.code:         { order :: pos_integer() % aka N
          , root :: #page{}
          }).
  
  %%%_* Creating an empty B-tree =================================================
  
  
negative.code: %%% Author      : Mikael Pettersson <mikael.pettersson@klarna.com>
  %%% Description : Erlang implementation of B-tree sets
  %%%
  %%% Copyright (c) 2016-2017 Klarna AB
  %%%
  %%% This file is provided to you under the Apache License,
  %%% Version 2.0 (the "License"); you may not use this file
  