That means that if I have two sets of numbers, let's say one set right over there, that's another set right over there, and if we view that first set as the domain of g, so if you start with some x right over here, g is going to map from that x to another value which we would call g of x, g of x. That's what the function g does. Now if h is the inverse of g, and frankly vice versa, then h could go from that point g of x back to x. So h would do this. H would get us back to our original value. So that's what the function h would do. And so we could view this point right over here, we could view it as x, so that is x, but we could also view it as h of g of x.