olemus
graafi üldistus: kaartel võivad olla ühised otspunktid;
formaalne definitsioon on analoogiline graafi omaga,
kuid kaarte hulk E võib olla multihulk

Wiktionary:
1. (graph theory) a set V (whose elements are called vertices or nodes), taken together with a multiset E, each of whose elements (called an edge or line) is a cardinality-two multisubset of V
Synonym: pseudograph
2. (graph theory, less commonly) a set V (as before), taken together with a multiset E, each of whose elements is a cardinality-two subset of V

ülevaateid
https://proofwiki.org/wiki/Definition:Multigraph

http://slideplayer.com/slide/736811/2/images/13/Directed+Multigraph+A+directed+multigraph+is+a+directed+graph+with+multiple+edges+between+the+same+two+distinct+vertices..jpg

https://mathworld.wolfram.com/Multigraph.html

https://en.wikipedia.org/wiki/Multigraph

rakendusi
https://www.cmu.edu/joss/content/articles/volume16/Shafie.pdf

https://thescipub.com/pdf/jcssp.2013.847.855.pdf

https://openproceedings.org/2016/conf/edbt/paper-168.pdf