In set theory, the naive definition of a set is "a collection of objects without an order or repetition". This means that $\{1\}=\{1,1\}=\{1,1,1,1,1,\ldots\}$ as well $\{1,2\}=\{2,1\}$.
There is a concept called multi-set in which order is of no importance, but repetition counts. I have never used these and I am not sure what would be the correct notation for them.
Lastly, there are also sequences (or ordered sets) in which both the order and the repetition are important, $\langle 1,1,1\rangle\neq\langle 1,1\rangle$ and $\langle 1,2\rangle\neq\langle 2,1\rangle$.
One final remark is that whenever you have an object you wish to work with the important thing is to define it clearly, be consistent with its notation and do your best to avoid overloading previously used symbols.