IntersectionOperatorPrecedence.swift

precedencegroup IntersectionOperatorPrecedence {
    associativity: left
}

infix operator ∩: IntersectionOperatorPrecedence

func ∩<T: Equatable> (left: [T], right: [T]) -> [T] {
    var intersection: [T] = []
    for value in left {
        if right.contains(value) {
            intersection.append(value)
        }
    }
    return intersection
}