I don’t understand how you expect the verification of a physical book to work. You’d have to scan/OCR the entire book to verify the signature.

Alternatively you could do a hash/signature per page to make verification of a single page easier.

Many public keys chain-linked with one master key - are just for example

Have a look at Merkle trees.

Was he aware of being a carrier of the gene before deciding to reproduce?

fzf fuzzy finder. Great tool to quickly find those files you were looking for.