anchor.diff:  
   remove(_Config) ->
   	T = example_insert(),
  -   {{{nil,1,7,a,nil},3,6,c,nil},2,6,b,{{nil,5,7,e,nil},6,6,f,{nil,7,8,g,nil}}} = ephemeral_trees:remove(T, 4).
  +   {{{undefined,1,7,a,undefined},3,6,c,undefined},2,6,b,{{undefined,5,7,e,undefined},6,6,f,{undefined,7,8,g,undefined}}} = ephemeral_trees:remove(T, 4).
   
   expire() ->
   	[{userdata, [{doc, "Expire example values used in paper."}]}].
   
   expire(_Config) ->
   	T = example_insert(),
  -	{nil,1,7,a,{nil,5,7,e,{nil,7,8,g,nil}}} = ephemeral_trees:expire(T, 6).
  +	{{{undefined,1,7,a,undefined},3,6,c,undefined},2,6,b,{{undefined,5,7,e,undefined},6,6,f,{undefined,7,8,g,undefined}}} = ephemeral_trees:expire(T, 6).
   
   overwrite_item() ->
   	[{userdata, [{doc, "Insert new item for existing key."}]}].
   
   overwrite_item(_Config) ->
   	T = example_insert(),
  -	{{{nil,1,7,a,nil},2,6,b,{nil,3,6,cbis,nil}},4,0,d,{{nil,5,7,e,nil},6,6,f,{nil,7,8,g,nil}}} = ephemeral_trees:insert(T, 3, 6, cbis).
  +	{{{undefined,1,7,a,undefined},2,6,b,{undefined,3,6,cbis,undefined}},4,0,d,{{undefined,5,7,e,undefined},6,6,f,{undefined,7,8,g,undefined}}} = ephemeral_trees:insert(T, 3, 6, cbis).
   
   overwrite_time() ->
   	[{userdata, [{doc, "Insert new time for existing key."}]}].
   
   overwrite_time(_Config) ->
   	T = example_insert(),
  -	{{{nil,1,7,a,nil},2,6,b,{nil,3,8,c,nil}},4,0,d,{{nil,5,7,e,nil},6,6,f,{nil,7,8,g,nil}}} = ephemeral_trees:insert(T, 3, 8, c).
  +	{{{undefined,1,7,a,undefined},2,6,b,{undefined,3,8,c,undefined}},4,0,d,{{undefined,5,7,e,undefined},6,6,f,{undefined,7,8,g,undefined}}} = ephemeral_trees:insert(T, 3, 8, c).
   
   %%---------------------------------------------------------------------
   %%  Internal functions
  
positive.code: 
  example_insert() ->
  	T1 = ephemeral_trees:insert(ephemeral_trees:new(), 1, 7, a),
  	{nil,1,7,a,nil} = T1,
  	T2 = ephemeral_trees:insert(T1, 2, 6, b),
  	{{nil,1,7,a,nil},2,6,b,nil} = T2,
  	T3 = ephemeral_trees:insert(T2, 3, 6, c),
  	{{nil,1,7,a,nil},2,6,b,{nil,3,6,c,nil}} = T3,
  	T4 = ephemeral_trees:insert(T3, 4, 0, d),
  	{{{nil,1,7,a,nil},2,6,b,{nil,3,6,c,nil}},4,0,d,nil} = T4,
  	T5 = ephemeral_trees:insert(T4, 5, 7, e),
  	T6 = ephemeral_trees:insert(T5, 6, 6, f),
  	T7 = ephemeral_trees:insert(T6, 7, 8, g),
  	{{{nil,1,7,a,nil},2,6,b,{nil,3,6,c,nil}},4,0,d,{{nil,5,7,e,nil},6,6,f,{nil,7,8,g,nil}}} = T7.
  
  
negative.code: 	[{userdata, [{doc, "Create new treap."}]}].
  
  new(_Config) ->
  	undefined = ephemeral_trees:new().
  
  insert() ->
  	[{userdata, [{doc, "Insert example values used in paper."}]}].
  