anchor.diff:  
   -behaviour(proper_statem).
   
  --export([ test/0
  -        , test/1
  +-export([ dotest/1
           , prop_seq/0
           ]).
   
  
positive.code: 
  -record(st, {set}).
  
  test() ->
    test(100).
  
  test(N) ->
    true = proper:quickcheck(?MODULE:prop_seq(), N),
    ok.
  
  
negative.code: %%%----------------------------------------------------------------
  %%% File        : btree_proper_tests.erl
  %%% Author      : Mikael Pettersson <mikael.pettersson@klarna.com>
  %%% Description : PropEr tests for Erlang implementation of B-tree sets
  %%%
  %%% Copyright (c) 2016-2018 Klarna Bank AB
  %%%
  %%% This file is provided to you under the Apache License,
  %%% Version 2.0 (the "License"); you may not use this file
  