Описание тега set-intersection
The intersection of two or more sets consists of the elements that those sets all have in common.
Set intersection is a mathematical operation defined upon sets.
The intersection of two or more sets is defined as the set of those elements that are present in all sets.
For example, let A = { 2, 3, 4 } and B = { 2, 4, 5 }.
The intersection of A and B is what the set of elements that A and B have in common: { 2, 4 }.
The symbol for intersection is ∩, so in our example we would write A ∩ B = { 2, 4 }