Iterate over &[1,2,3,4,5,6,7,8,9] to receive `&[1,4,7]` then `&[2,5,8]` then `&[3,6,9]`

I'll send you to the book for more about that: https://doc.rust-lang.org/stable/book/ch04-02-references-and-borrowing.html#mutable-references

But mutable references have one big restriction: you can have only one mutable reference to a particular piece of data at a time.