x, y: Pair of compatible data frames. A pair of data frames is compatible if they have the same column names (possibly in different orders) and compatible types.
...: These dots are for future extensions and must be empty.
Base functions
intersect(), union(), setdiff(), and setequal() override the base functions of the same name in order to make them generic. The existing behaviour for vectors is preserved by providing default methods that call the base functions.