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Get the book
One listing. Both formats live inside it. Amazon will ask you which.[1]
Paperback
£10.99
The physical object. Does not update, sync, or expire.
Kindle
£5.99
Arrives in about four seconds. Technically leased, in the way all ebooks are, which nobody reads the terms for.
[1] 100% certain these are the correct prices, as of the last time I was told them. Amazon decides which format you see first, not me.