Possessive “de” with partitive “de”

Question

I understand that you can often translate the English some with the French partitive de like so:

I met some vegetarians → J’ai rencontré des végétariens.

If I instead said:

J’ai rencontré les végétariens

I assume that would have a different meaning, maybe that I met all of the vegetarians within some particular context.

How do I distinguish between these two if I add de for another reason, such as to mark the possessive? For example, how do I translate this:

I read a book from some vegetarians.

It seems like this could maybe need two de’s like this:

J’ai lu un livre de des végétariens.

However this sounds very odd to me. If I changed it to just un livre des végétariens, would that be indistinguishable from the book belonging to les végétariens? Is there a better way to say this?

Answer 1

J'ai rencontré les végétariens

means "I met the vegetarians".

J'ai lu un livre de des végétariens

is not grammatical. You might say:

J'ai lu un livre de végétariens

but it is ambiguous, it might mean as well "I read a book about vegetarians." As you suspected:

J'ai lu un livre des végétariens

is also ambiguous and can mean "a book belonging to..."

To make clear the book was written by some vegetarians, you might say:

J'ai lu un livre écrit par des végétariens.