1 – Read his blog: http://unenumerated.blogspot.co.uk every single post there is a “Bitcoin white paper” in it’s own right
2 – In his post about Bitgold (http://unenumerated.blogspot.co.uk/2005/12/bit-gold.html) he’s mentioning that unfortunately “The main problem […] is that proof of work schemes depend on computer architecture, not just an abstract mathematics based on an abstract “compute cycle.”. In the Bitcoin white paper he states that “The proof-of-work also solves the problem of determining representation in majority decision making. If the majority were based on one-IP-address-one-vote, it could be subverted by anyone able to allocate many IPs. Proof-of-work is essentially one-CPU-one-vote”.
3 – Bitcoin white paper doesn’t reference Nick Szabo Bitgold despite the fact that Bitgold is extraordinarily similar to Bitcoin
4 – http://unenumerated.blogspot.co.uk/2006/12/law-embedded-in-world.html in this (apparently) silly post Nick is subtly referencing the double spending problem and how it’s solved. The first car (transaction) passes trough (get confirmed), the second malicious car (double spend attempt) get blocked
5 – Silly proof: SN = NS 🙂