changes (suggested) by Soren Larsen
diff --git a/Doc/lib/libsys.tex b/Doc/lib/libsys.tex
index fc71139..ffda68d 100644
--- a/Doc/lib/libsys.tex
+++ b/Doc/lib/libsys.tex
@@ -88,7 +88,7 @@
as thread switches and signal handlers. The default is 10, meaning
the check is performed every 10 Python virtual instructions. Setting
it to a larger value may increase performance for programs using
-threads. Setting it to a value <= 0 checks every virtual instruction,
+threads. Setting it to a value $\leq 0$ checks every virtual instruction,
maximizing responsiveness as well as overhead.
\end{funcdesc}