Christoph Bluth of the University of Bradford stated that "a no-fly zone does not mean that no aircraft are permitted to fly, because it is enforced by aircraft that constantly patrol the skies," since aircraft designated friendly under identification friend or foe systems could be spared, but that "nuclear deterrence is working – it is deterring NATO, as western leaders are unsure about the rationality of Russia's leadership," adding that "it is important to be clear that a no-fly zone over Ukraine is a different proposition compared with other conflicts, such as those in Iraq and Syria."[27]