**What’s happening:**

One of the tests has the inputs of: [1, 2, 5], [2, 3, 5], [3, 4, 5]

With the expected output to be: [1, 4, 5]

But that doesn’t seem to make sense because 5 appears in all of the sets. Why is it included as the answer? I thought the solution would be [1,4]

Can anyone explain?

**My code so far**

```
function sym(args) {
let sets = Array.from(arguments);
let values = sets.reduce( (a, b) => { return a.concat(b) } );
values.sort( (a,b) => { return a-b })
console.log(values)
let filtered_values = values.filter( (value) => {
let first_index = values.indexOf(value);
if( values.indexOf(value, first_index + 1) === -1 ) { return value }
})
return filtered_values
}
sym([1, 2, 3], [5, 2, 1, 4]);
```

**My browser information:**

My Browser User Agent is: `Mozilla/5.0 (X11; Linux x86_64; rv:57.0) Gecko/20100101 Firefox/57.0`

.

**Link to the challenge:**

https://www.freecodecamp.org/challenges/symmetric-difference