If and are types, then so is their Cartesian product, , whose elements are ordered pairs, with and . For example consists of the points with integer co-ordinates in the plane. If then there are several common ways to denote the first and second components of the pair. Here are some of the common ways: first, 1of or for the first, and second, 2of or for the second. We have An n-ary product, say is regarded as . In general is . Given , the 2nd component is and the 3rd is . We'll see these selectors in the definition of an automaton (section 4.1).