I am currently trying the symmetric difference challenge in the advanced algorithm scripting section. If I understood correctly, then the symmetric difference is the collection of elements contained in either one of a certain number of collections, but NOT in all of them.

Then how is sym([1, 2, 5], [2, 3, 5], [3, 4, 5]) supposed to return [1, 4, 5]? It says so in the test results of the challenge, but the 5 is an all three of the aforementioned arrays and, according to the definition, then it would NOT be returned.

What did I get wrong?

Thank you