Fixes/Workarounds for bugs in Mathematica's LaTeX Export: Problems with Subsuperscript and with nonsensical \left and \right tags.

texexpression.py

#!/usr/bin/env pyton3

import re
import sys

subsup_regex = re.compile(r"\\text\{Subsuperscript\}\[([^\],]*),([^\],]*),([^\],]*)\]")

minimal_braces = True


def replace_subsup(string):
    """Replace one subsuperscript with correct LaTeX code.
    Returns (replaced string, bool: did we replace something)
    """
    match = subsup_regex.search(string)
    if not match:
        return string, False
    expr, sub, sup = match.groups()
    if len(expr) > 1 or not minimal_braces:
        expr = "{"+expr+"}"
    if len(sub) > 1 or not minimal_braces:
        sub = "{"+sub+"}"
    if len(sup) > 1 or not minimal_braces:
        sup = "{"+sup+"}"
    matched = match.string[match.span()[0]:match.span()[1]]
    replacement = r"{expr}_{sub}^{sup}".format(expr=expr, sub=sub, sup=sup)
    return string.replace(matched, replacement), True


def replace_no_delim(string):
    """ E.g. when doing TeXForm[Abs[1+Subscript[g,A]]^2], Mathematica
    produces 
        
        \\left\\left| g_A+1\\right\\right| {}^2
    
    with superfluous \\left, \\right with no delimeter. 
    Here we try to delete those. 
    """
    string=string.replace("\\left\\","\\")
    string=string.replace("\\right\\","\\")
    return string

def replace_all(string):
    """Generates correct LaTeX code"""
    string = replace_no_delim(string)
    continue_ = True
    while continue_:
        string, continue_ = replace_subsup(string)
    return string


if __name__ == "__main__":
    if len(sys.argv) == 1:
        print(replace_all(str(sys.stdin.read())))
    else:
        print(replace_all("\n\n".join(sys.argv[1:])))

texexpression.wl

fixLatexErrors[string_]:=
Module[{ret},
	ret=RunProcess[{"python3",FileNameJoin[{ToString@NotebookDirectory[],"texexpression.py"}], string},"StandardOutput"];
	Return[StringTake[ret,;;-2]];(*split last newline*) 
];

description here: http://www.lieret.net/2018/01/04/mathematica-latex-bugs/