You are demanding to be able to read a random line in the middle of a book and understand everything. This is stupoid, the book/article/theory will have a secti

You are demanding to be able to read a random line in the middle of a book and understand everything. This is stupoid, the book/article/theory will have a section that defines everything is used. You have same shit on JS where + can mean do a numeric addition or it can mean concat 2 strings and other powerful languages will allow you to have + enhanced so you can use it to add matrices,vectors,fractions time intervals etc. If you want for example to understand the fundamental theorem of statistics you can read only it and his proof you need to read and understand everything in the book before it.