He said: "The only thing stopping me [signing them] is that I have made this film and I have a bloody book to finish."Sir Terry Pratchett begins process that could lead to assisted suicide (Thanks, Fipi Lele!)
But he stressed that he was as yet still undecided whether he would eventually take his own life.
He said he changed his mind "every two minutes" but added that if he did choose to die would prefer to do so in England and in the sunshine.
Sir Terry, creator of the Discworld novels, was 60 when he was diagnosed with terminal condition and has since campaigned passionately for a change in the law to allow assisted suicide in Britain.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.