It has now fallen into a pattern that every time he is set for a significant overture towards Washington, North Korean leader Kim Jong Un makes a point of getting advice from China ahead of the meeting. His latest trip, apparently coinciding with his 35th birthday, saw the Kim dynast travel in a special bullet-proof train on a 20-hour trip to Beijing, during which he met Chinese President Xi Jinping twice. Since his first, surprise visit to the Chinese capital in March last year, this is the third time he has travelled to China. Smaller nations typically tend to be more mindful of the principle of reciprocity in bilateral relations, but this has not seemed to matter to Mr Kim, given that Mr Xi has yet to visit Pyongyang. In any case, a second summit meeting between Mr Kim and US President Donald Trump seems to be on the cards, at a venue and date yet to be disclosed.

Beijing seems to endorse this. The Xinhua news agency quoted Mr Xi as saying he supported further dialogue and hoped Pyongyang and Washington would "meet each other halfway". Since Washington demands complete, verifiable and irreversible dismantlement of the North's nuclear programme and Pyongyang, in turn, seeks a phased denuclearisation in tandem with the lifting of economic sanctions, it is not clear where Beijing sees the middle line. Nevertheless, China's backing is significant. The complications arise from the vagueness of the agreement that the US and North Korea signed at their historic first summit in Singapore last June. The second paragraph of that document contained a vague declaration that Mr Trump "committed to provide security guarantees to the DPRK, and Chairman Kim Jong Un reaffirmed his firm and unwavering commitment to complete denuclearisation of the Korean peninsula". To Mr Kim's ears, this sounded like the promise of a peace treaty to replace the armistice of 1953. Denuclearising the Korean peninsula could also be taken to mean that all nuclear weapons - including those presumably in US hands - will be removed from the region.