http://www.mathsisfun.com/sets/function … ition.html http://www.mathsisfun.com/sets/function … ition.html http://www.mathsisfun.com/sets/function … ition.html http://www.mathsisfun.com/sets/function … ition.html composition of functions http://www.mathsisfun.com/sets/function … ition.html http://www.mathsisfun.com/sets/function … ition.html http://www.mathsisfun.com/sets/function … ition.html