anchor.diff:                                        )
                        end, lists:seq(1,100)).
   
  -list_shrink2_testx() ->
  -    %% test that a list doesn't easily end in a local 'smallest counterexample'
  -    true = lists:all(fun(_) ->
  -                             [[]] = triq:counterexample(
  -                                       ?FORALL(L, list(oneof([a,b])),
  -                                               not is_pairs_list(L))
  -                                      ),
  -                             true
  -                     end, lists:seq(1,100)).
  -
  -is_pairs_list([])      -> true;
  -is_pairs_list([X,X|T]) -> is_pairs_list(T);
  -is_pairs_list(_)       -> false.
  +%list_shrink2_testx() ->
  +%    %% test that a list doesn't easily end in a local 'smallest counterexample'
  +%    true = lists:all(fun(_) ->
  +%                             [[]] = triq:counterexample(
  +%                                       ?FORALL(L, list(oneof([a,b])),
  +%                                               not is_pairs_list(L))
  +%                                      ),
  +%                             true
  +%                     end, lists:seq(1,100)).
  +%
  +%is_pairs_list([])      -> true;
  +%is_pairs_list([X,X|T]) -> is_pairs_list(T);
  +%is_pairs_list(_)       -> false.
   
   oneof_test() ->
       [{X,Y}] = triq:counterexample(
  
positive.code: counterexample_test() ->
      Counterexample = triq:counterexample(xprop_delete()),
      ?assertEqual(false, triq:check(xprop_delete(), Counterexample)).
  
negative.code: %% use eunit
  -include_lib("eunit/include/eunit.hrl").
  
  
  boolean_test() ->
      Unique = fun ordsets:from_list/1,
  