EDIT: It appears the evidence I listened to about is an ordinary reference specified here numerous times :) I stated which the proof itself is considerably less valuable than an outline for me as I am aware only "physics degree maths". 知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。 Example of wood carving in Tomsk https://bihlmayermedia-bilder.com/1-advent/