math-mode
I have tried searching for \right. in many places but have not been able to decipher its magical properties. Many texts use the arcane symbol but none that I have found explain it. The composition of the symbol with its elusive period, has also made the search problematic.
Please help!
I stumbled upon the correct markup used in Wikipedia's article on geometric algebra. I looked at the code and found the symbol is given by \lrcorner. \llcorner is the same thing but flipped horizontally.
Your preamble is a bit messy.
Loading mathabx and amssymb along with newtxmath is useless: if you load mathabx before newtxmath, most of the symbols will be redefined; in the other order, mathabx will override most of newtxmath symbols.
Also skull allocates a math symbol font just for one symbol. It doesn't seem worthy it and it's easy to do without wasting a math group.
The package loading order is very important; in some cases you get conflicts. In particular, bm should be loaded after math font packages and after amsmath.
Don't load both babel and polyglossia: they fight each other.
\documentclass[10pt,a4paper]{book}
\usepackage{fix-cm}% just to avoid some spurious messages
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{amsthm}
\usepackage{thmtools}
\usepackage{wasysym}
%\usepackage{skull} % see later
\usepackage{newtxmath}
%\usepackage{amssymb} % not with newtxmath
%\usepackage{mathabx} % not with newtxmath
\usepackage{bm}
\usepackage{lscape}
\usepackage{ragged2e}
\usepackage{faktor}
\usepackage{xfrac}
\usepackage{enumitem}
\usepackage{yfonts}
\usepackage{comment}
\usepackage{graphicx}
\usepackage{wrapfig}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric}
\usepackage{lipsum}
%\usepackage[russian]{babel} % either babel or polyglossia
\usepackage{polyglossia}
\setmainlanguage{russian}
\setmainfont{Georgia}
\newfontfamily\cyrillicfont{Georgia}
%%% Loading a math symbol font for just one symbol is a big waste
%%% The following lines do the same as skull.sty
\DeclareFontFamily{U}{skulls}{}
\DeclareFontShape{U}{skulls}{m}{n}{ <-> skull }{}
\newcommand{\skull}{\text{\usefont{U}{skulls}{m}{n}\symbol{'101}}}
\begin{document}
\[
\bm{\Phi}+\skull
\]
\end{document}
Finally, update your TeX system: with XeLaTeX and a properly crafted preamble it's quite rare to incur in the “Too many math fonts” error.
Best Answer
It produces an "invisible" delimiter that is used to match a corresponding
\left. You can use it when you need a delimiter only on one side of the expression.lshortalso describes it.An example of such usage would be typesetting a multi-case function definition: with a figure brace on the left and nothing on the right.
(NOTE: This is only an example and has improper spacing. In real life you would use the
casesenvironment for this.)