proper LaTeX setup (amending 41b387d47739);

--- a/src/HOL/IMP/document/root.tex	Tue Dec 10 16:37:09 2024 +0100
+++ b/src/HOL/IMP/document/root.tex	Tue Dec 10 19:23:55 2024 +0100
@@ -1,5 +1,6 @@
 \documentclass[11pt,a4paper]{article}
 \usepackage[T1]{fontenc}
+\usepackage{amssymb}
 \usepackage{isabelle,isabellesym}
 \usepackage{latexsym}
 % this should be the last package used