2. There is in addition a principle to the effect that a special rule prevails over a general rule (lex specialis derogate legi generali), so that, for example, treaty rules between states as lex specialis would have priority as against general rules of treatyor customary law between the same states, although not if the general rule in question was one of jus cogens. (Malcolm N Shaw, International Law, (6thedn. Cambridge University Press, Cambridge 2008.at p124)