Unterschneidung für kursives Griechisch in TeX Gyre Termes Math

\RequirePackage{ifthen}
\RequirePackage{ifxetex,ifluatex}
\newif\ifxetexorluatex
\ifxetex
  \xetexorluatextrue
\else
  \ifluatex
    \xetexorluatextrue
  \else
    \xetexorluatexfalse
  \fi
\fi
\documentclass{article}
\ifxetexorluatex
\tracinglostchars=2
\usepackage{fontspec}%% needed only for xelatex.
\usepackage[american,british,french,norsk,german,ngerman]{babel} % warning: last language option will be chosen for fixed text of environments like example or definition (in svmono)
\usepackage{mathtools}%%% loads amsmath internally
\mathtoolsset{mathic=true} %%% See http://tex.stackexchange.com/a/3496
\usepackage{amssymb}
\usepackage[math-style=ISO]{unicode-math}
\setmainfont[Ligatures=TeX]{TeX Gyre Termes}
\setsansfont{TeX Gyre Heros}[Scale=0.88]%%% Somewhat ok.
\setmonofont{TeX Gyre Cursor}%%% No explicit turning on ligatures for the monospaced font.
\setmathfont[Ligatures=TeX]{TeX Gyre Termes Math}
\setmathfont[Ligatures=TeX,range={\setminus}]{Asana Math}%%% Set difference
\setmathfont[Ligatures=TeX,Extension=.otf,range={"2982},BoldFont=XITSMath-Bold]{XITSMath-Regular}%%% Z notation type colon ⦂ (U+2982). (Big tall oblong ⫿ also exists in XITS, but is slightly smaller in STIX.)
\setmathfont[Ligatures=TeX,Extension=.otf,range={"2AFF}]{STIX-Regular}%%% Big tall oblong ⫿ (U+2AFF). Slightly smaller than in XITS.
\else
\usepackage[T2A,T1]{fontenc}%%% The fontenc package is explicitly loaded with the T2A,T1 argument simply to avoid the warning of babel about missing T2A in the log. As for the order of loading, David Carlisle says in https://tex.stackexchange.com/questions/241452/generating-a-template/241479#241479 that fontenc produces information needed by inputenc (which, however, delays processing till the beginning of the document, which makes the order of these two packages irrelevant). Moreover, in the examples in the documentation of newtx fontenc is always loaded before newtx.
\usepackage[utf8]{inputenc} % Native LaTeX umlaut support
\usepackage[american,british,french,norsk,german,ngerman]{babel} % warning: last language option will be chosen for fixed text of environments like example or definition (in svmono)
\usepackage{newtxtext}% Load it after babel according to Michael Sharpe's newtx manual from Dec 14, 2017.
\usepackage[slantedGreek]{newtxmath}%% Should be loaded after the text font according to its manual. The default uppercase Greek letters should be slanted according to the Springer manual.
\usepackage{courier}
\usepackage{mathtools}%%% loads amsmath internally
\mathtoolsset{mathic=true} %%% See https://tex.stackexchange.com/a/3496
\fi
\usepackage[babel=true,verbose=errors]{microtype}%%% Microtype documentation says it determines the best settings itself, depending on the compiler and the driver.
\begin{document}
\(\Delta(\sigma)\)

\(\tau_0, \tau_1, \dotsc, \tau_9, \tau_i, \tau_j, \tau_k, \tau_{\mathrm{k}}, \tau_n, \tau_{i+1}, \tau_{i-1}\)

\(\pi_0, \pi_1, \dotsc, \pi_9, \pi_i, \pi_j, \pi_k, \pi_{\mathrm{k}}, \pi_n, \pi_{i+1}, \pi_{i-1}\)

\(\sigma_0, \sigma_1, \dotsc, \sigma_9, \sigma_i, \sigma_j, \sigma_k, \sigma_{\mathrm{k}}, \sigma_n, \sigma_{i+1}, \sigma_{i-1}\)
\end{document}