diff --git a/Admin/polyml/README b/Admin/polyml/README
--- a/Admin/polyml/README
+++ b/Admin/polyml/README
@@ -1,52 +1,58 @@
 Poly/ML for Isabelle
 ====================
 
 This compilation of Poly/ML (https://www.polyml.org) is based on the
 source distribution from
 https://github.com/polyml/polyml/commits/fixes-5.8.2 up to commit
 e6a463e1614f.
 
 The Isabelle repository provides an administrative tool "isabelle
 build_polyml", which can be used in the polyml component directory as
 follows.
 
 * Linux:
 
   $ isabelle build_polyml -m32 -s sha1 src
   $ isabelle build_polyml -m64 -s sha1 src
 
 * macOS:
 
   $ isabelle build_polyml -m32 -s sha1 src
   $ isabelle build_polyml -m64 -s sha1 src
 
 * Windows (Cygwin shell)
 
   $ isabelle build_polyml -M /cygdrive/c/msys64 -m32 -s sha1 src
   $ isabelle build_polyml -M /cygdrive/c/msys64 -m64 -s sha1 src
 
 
 Building libgmp on macOS
 ========================
 
 The build_polyml invocations above implicitly use the GNU Multiple Precision
 Arithmetic Library (libgmp), but that is not available on macOS by default.
 Appending "--without-gmp" to the command-line omits this library. Building
 libgmp properly from sources works as follows (library headers and binaries
 will be placed in /usr/local).
 
 * Download:
 
-  $ curl https://gmplib.org/download/gmp/gmp-6.1.2.tar.xz | xz -dc | tar xf -
-  $ cd gmp-6.1.2
+  $ curl https://gmplib.org/download/gmp/gmp-6.2.1.tar.bz2 | tar xjf -
+  $ cd gmp-6.2.1
 
 * build:
 
   $ make distclean
+
+  #Intel
   $ ./configure --enable-cxx --build=core2-apple-darwin"$(uname -r)"
+
+  #ARM
+  $ ./configure --enable-cxx --build=aarch64-apple-darwin"$(uname -r)"
+
   $ make && make check
   $ sudo make install
 
 
         Makarius
-        07-May-2021
+        11-May-2021