All four nuclear nations
There are 9 nuclear nations: France, the UK, China, Russia, the USA, India, Pakistan, Israel, and North Korea. Out of those, the first 5 are all recognized in the NPT. India, Pakistan, and Israel never signed the NPT. North Korea withdrew. Which 4 are you talking about?
C'est magnifique, mais ce n'est pas l'Informatique. -- Bosquet [on seeing the IBM 4341]