Full Idea
The 'union' of two sets is a set containing all the things in either of the sets
Gist of Idea
The 'union' of two sets is a set containing all the things in either of the sets
Source
Graham Priest (Intro to Non-Classical Logic (1st ed) [2001], 0.1.8)
Book Reference
Priest,Graham: 'Introduction to Non-Classical Logic' [CUP 2001], p.-6