# AMPL duplicate member "x" for set "y", how to fix it **URL:** \ **Category:** Support\ **Tags:** displays-results, sets-and-indexing, errors-and-messages, files-preprocessing, modeling\ **Created:** [April 5, 2023, 8:55am UTC](https://discuss.ampl.com/t/ampl-duplicate-member-x-for-set-y-how-to-fix-it/474 "2023-04-05T08:55:53Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![fdabrandao](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.ampl.com/fdabrandao/32/63_2.png) [@fdabrandao](https://discuss.ampl.com/u/fdabrandao)\ **Post date:** [April 5, 2023, 9:19am UTC](https://discuss.ampl.com/t/ampl-duplicate-member-x-for-set-y-how-to-fix-it/474/2 "2023-04-05T09:19:07Z")
Hi @Ares_Inglada_Grano, Without specifying the arity of a set it defaults to 1 and any repeated value in the data section will then be a duplicate. You need to specify the arity of the set (i.e., `set path_intersections dimen 2;`) as follows: ```ampl set path_intersections dimen 2; data; set path_intersections := 1439 5 1439 74243 1441 5 1441 89 1441 90; display path_intersections; ``` This will produce the following output: ```auto set path_intersections := (1439,5) (1439,74243) (1441,5) (1441,89) (1441,90); ``` Also replied on [AMPL duplicate member "x" for set "y", how to fix it - Stack Overflow](https://stackoverflow.com/questions/75937400/ampl-duplicate-member-x-for-set-y-how-to-fix-it) --- _[View the full topic](https://discuss.ampl.com/t/ampl-duplicate-member-x-for-set-y-how-to-fix-it/474)._