secondary sources:
https://baike.baidu.com/item/%E6%89%98%E6%B4%9B%E8%8C%A8%E5%9F%BA%E4%B8%BB%E4%B9%89
https://www.ecured.cu/Le%C3%B3n_Trotsky
http://www.cyberussr.com/rus/trotsky-bse-e.html
https://kommynist.ru/%D0%A2%D1%80%D0%BE%D1%86%D0%BA%D0%B8%D0%B9,_%D0%9B%D0%B5%D0%B2_%D0%94%D0%B0%D0%B2%D0%B8%D0%B4%D0%BE%D0%B2%D0%B8%D1%87
