avoid jdk-11.0.6+10: it shows problem "S8217731: Font rendering and glyph spacing changed from jdk-8 to jdk-11" https://bugs.openjdk.java.net/browse/JDK-8217731 even though the changelog claims to have resolved this;
#!/usr/bin/env bash
#
# Author: Makarius
#
# DESCRIPTION: setup OCaml via OPAM
set -e
if [ -d "$ISABELLE_OPAM_ROOT/$ISABELLE_OCAML_VERSION/bin" ]
then
isabelle_opam switch -y "$ISABELLE_OCAML_VERSION"
elif [ -e "$ISABELLE_OPAM_ROOT/config" ]
then
isabelle_opam switch create -y "$ISABELLE_OCAML_VERSION"
else
isabelle_opam init -y --disable-sandboxing --no-setup --compiler="$ISABELLE_OCAML_VERSION"
fi
isabelle_opam install -y zarith