It is true, I am not very clear about the concept of composition. But thanks for making me understand. I read on Wikipedia (in the Push the Button album article) that Tom handled keyboards, samples, synthesizers and programming, while Ed handled keyboards, guitar, bass and engineering. Perhaps Tom is sometimes the engineer, other times Ed is the engineer and in others both are in charge of engineering (along with Steve Dub). As the chemical brothers have Steve Dub, Fatboy Slim (of whom I am fan number 1 and who is a good friend of the Chemical Brothers) has Simon Thornton and The Prodigy has Neil Mclellan.