Wow, very sad to hear this. I am a big fan of Professor Graham. I owned many of his books - Magical Mathematics, Rudiments of Ramsey Theory, Concrete Mathematics, Handbook of Combinatorics. I attended an AMS conference in San Diego a while back and asked him to sign my Erdos on Graphs book after listening to his talk. Professor Chung happened to be around and he waved her over to sign my book too.