Collection

union: denote A∪B (or B∪A), denote A∪B (or B∪A), read as "A and B" (or "B and A"), and denote A∪B (or "B and a"). That is, A∪B={x|x∈A, or x∈B}

Example, total set U={1,2,3,4,5} A={1,3,5} B={1,2,5}.

The two collections contain five elemental elements: 1,2,3,4,5, regardless of the number of occurrences of elemental, as long as elemental appears in these two collections. then it says A∪B={1,2,3,5}. The shaded part of the figure is A∩B.

intersection: An elemental Collection belonging to A and B elemental is called A and B intersection (set), denote A∩B (or B∩A), read as "A intersects B" (or "B intersects A"), That is, A∩B={x|x∈A and x∈B}

Example, total set U={1,2,3,4,5} A={1,3,5} B={1,2,5}. then since both A and B have 1,5, A∩B={1,5}.

difference: An elemental Collection that belongs to A but not to B is called A and B difference (set)