Can I point out that the notes for this section are not ideally presented ?
It would help if combinations with repititions were included in the Section 2 Course notes – which apart from that is a handy reference to the different functions. Having it “hidden” in another document (especially as it’s the hardest formula to remember) is a littel irritating – even if that separate document is giving a full explanation of it’s derivation.
Sorry for the inconvenience!
I’ll make sure to add the combinations with repetition formula to the Combinatorics course notes and upload the updated file shortly.