[DavidFriedman]

Sounds like an interesting area. I will try and look it up. Thanks

Originally Posted by Ren Ren

I like your question, but I don't have an answer yet. In the North of Vietnam, along the border with China, paired objects are widespread. But I am not sure that the same customs exist in the Northwest of Vietnam, on the border with Laos. This needs to be checked.
I just started to discover this region of Vietnam. This is an amazing place with a huge natural and ethnic diversity. I heard from biologists that in this region there are species of animals and plants typical of the West - for India and Indo-China, for the East - for China and East Asia, and for the North - for Tibet, Mongolia and even Siberia. Also, several dozen small peoples live there, speaking the languages ​​​​of four or even five large language groups. On our planet, such diversity is probably found only in the Caucasus. But it is still a little explored and hard to reach place, and many discoveries will be made there.