Nikita Fedyashev said almost 2 years ago on Grab Bag of Ruby and Ruby on Rails Tricks :
11:08 "this is going to do a union between them" I guess what David meant to say was "an intersection between them" instead

> [1, 2, 3] & [3, 4]

Same in the comment
"# Array Setters, Union and Subtraction" => "# Array Setters, Intersection and Subtraction"