Ask HN: What is the most obscure book you own?

Just had an interesting conversation about book collecting this weekend: we asked each other which of their books is so obscure or rare that it's unlikely anybody else you know owns a copy.

For me, it's a printed copy of von Neumans "First Draft of a Report on the EDVAC", the groundwork for modern computer architecture. Bought it from Kronecker Wallis, a tiny Spanish publisher.