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A relative (who is no longer living) wrote a number of autobiographical pieces which I would like to publish in a book. They're very good but they need a fair amount of editing. I would like to include some chapters written by myself, that would supplement the relative's memories. How to I put my name on the cover and title page? If I were only writing one chapter, I could call that an epilogue and say:
edited and with an epilogue by Aparente
But this won't work if I contribute three or four chapters.
I remember reading a book called A Monster Calls, which had the same thing going on. The original idea was from Siobhan Dowd, but she died, and the book was completed by Patrick Ness. I would do something similar:
Originally written by X. Completed by Y.
I would have an afterword detailing the writing of the novel, and the parts you contributed to as well as edited to make the 'completion' more clear.
(I have also seen "as told to," which to me means the person in question sat for multiple interviews and the writer collated and wrote everything down in first person even though it wasn't the writer's story.)