Philip K. Dick and Abraham Abulafia
From The Selected Letters of Philip K. Dick: 1977-1979 (p. 225):
[TO CHARLES N. BROWN, Locus] April 23, 1979
Dear Charles,
This is to let you know that after four years of research and work I have finally finished my new novel VALIS for Bantam. In the writing I collaborated with the spirit of the 13th century Jewish Kabbalist Abraham ben Samuel Abulafia who seizes control of me from time to time, as circumstances require.
Hope all is well with you.
Cordially,
Philip K Dick
HT: Alan Brill, Avi Solomon, and Philip K. Dick and Religion
BLT 
A friend read this post and replied, “Well, now we know who the actual writer was. I had suspected PKD had help.”
Craig, I suspect this post was inspired by this one.
So do ghosts write but only humans translate?
I once gave testimony in a foreign court, and that court’s rules allowed me to specify if I wished to take my oath with my hand on a holy book other than the Protestant Bible. I gather that some people request books such as the Koran, Book of Mormon, Catholic Bible, etc.
I was sorely tempted to request to take the oath with my hands on the Valis trilogy.