anchor.diff:  swap_7_elem_list_test_() ->
       {"swap [1,2,3,4,5,6,7] must halt and equal expected",
        ?_assertEqual(
  -	[[7,3,1,2,6,5,4],
  +	[],lists:subtract([[7,3,1,2,6,5,4],
   	 [7,3,1,2,5,4,6],
   	 [7,3,1,2,4,6,5],
   	 [7,1,2,3,6,5,4],
  
positive.code: -module(swap).
  -export([swap/1, swap_2500_profile/0]).
  -include_lib("eunit/include/eunit.hrl").
  -import(dist, [dist/2]).
  -import(umerge, [umerge/2]).
  
  swap(L) ->
      swap(L, []).
  
  swap([], P) ->
  
negative.code: 	 [7,2,3,1,6,5,4],
  	 [7,2,3,1,5,4,6],
  	 [7,2,3,1,4,6,5]],
  	swap2([1,2,3,4,5,6,7])))}.
  
  swap_tail2_7_elem_list_test_() ->
      {"swap [1,2,3,4,5,6,7] must halt and equal expected",
       ?_assertEqual(
  	[[1,3,2,5,4,6,7],
  	 [1,3,2,5,4,7,6],
  	 [2,1,3,5,4,6,7],
  	 [2,1,3,5,4,7,6],
  	 [3,2,1,5,4,7,6],
  	 [3,2,1,5,4,6,7],
  	 [3,2,1,4,5,6,7],
  	 [3,2,1,4,5,7,6],
  	 [2,1,3,4,5,7,6],
  	 [2,1,3,4,5,6,7],
  	 [1,3,2,4,5,7,6],
  	 [1,3,2,4,5,6,7]],
  	swap_tail2([1,2,3,4,5,6,7]))}.
  
  swap2_8_elem_list_test_() ->
      {"swap [1,2,3,4,5,6,7,8] must halt and match certain expectation",
       ?_assertMatch([H|_] when H == [5,6,4,2,1,3,8,7], swap2([1,2,3,4,5,6,7,8]))}.
  
  swap_tail2_8_elem_list_test_() ->
      {"swap [1,2,3,4,5,6,7,8] must halt and match certain expectation",
       ?_assertMatch([H|_] when H == [7,8,5,6,3,4,2,1], swap_tail2([1,2,3,4,5,6,7,8]))}.
  
  
  %swap_2500_test_() ->
  %    {"Swap '[1..2500]' must halt", 
  %    ?_assertMatch([[L|_]|_] when length(L) == 2500, swap_tail2(lists:seq(1, 2500)))}.
  
  
  %% swap([]) ->
  