Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am trying to describe the edges of an undirected graph that contains loops. On Wikipedia they are characterized as 2-multisets, meaning it has two elements which can be identical, and the order is not important. I never heard of that term, and find no reference to it anywhere else, so I am not sure whether it is OK to use it in my thesis. Can anyone clear that up for me?

share|cite|improve this question
Technically any term that you have well defined can be used in your thesis. – picakhu Jan 22 '11 at 18:25
To illustrate what Picakhu said, see and the Physics Today article by David Mermin linked therein. (Note: using a term and having it taken up by the community seriously are two different things.) – Willie Wong Jan 22 '11 at 18:35
Or, for an older and more widely known term, see – Ilmari Karonen Jun 17 '12 at 15:59
This all seems to assume there can't be more than one edge between two vertices. – Michael Hardy Jun 17 '12 at 17:37
@MichaelHardy: Hmm? If there can be multiple edges between a pair of vertices, then the edges of the graph form a multiset rather than a set, but each edge is still an unordered pair (or a "2-multiset", if you prefer). – Ilmari Karonen Jun 17 '12 at 22:14
up vote 1 down vote accepted

Yes. See the Wikipedia article on multisets and the many references therein for where it has occurred previously in literature.

(Note, in the context, a 2-multiset merely means a multiset containing 2 elements.)

share|cite|improve this answer

As Willie Wong notes, it's a perfectly valid term, but at least I personally would find "unordered pair" more natural than "2-multiset".

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.