Numerical 3-dimensional matching
Numerical 3-dimensional matching is an NP-complete decision problem. It is given by three multisets of integers X {\displaystyle X} , Y {\displaystyle Y} and Z {\displaystyle Z} , each containing k {\displaystyle k} elements, and a bound b {\displaystyle b} .
Source: Wikipedia — Numerical 3-dimensional matching (CC BY-SA 4.0)