Consistently use \POSIX{} to denote POSIX. There were at least two different
ways to do it previously (not counting module names).
diff --git a/Doc/lib/libthread.tex b/Doc/lib/libthread.tex
index fcee360..911c145 100644
--- a/Doc/lib/libthread.tex
+++ b/Doc/lib/libthread.tex
@@ -13,7 +13,7 @@
\index{semaphores, binary}
The module is optional. It is supported on Windows NT and '95, SGI
-IRIX, Solaris 2.x, as well as on systems that have a POSIX thread
+IRIX, Solaris 2.x, as well as on systems that have a \POSIX{} thread
(a.k.a. ``pthread'') implementation.
\index{pthreads}
\indexii{threads}{posix}