I got the following message on upgrading opam, and I am not sure what to do. Regards, Luc.
$ opam upgrade Everything as up-to-date as possible (run with --verbose to show unavailable upgrades). The following packages are not being upgraded because the new versions conflict with other installed packages: - camlp4.4.07+system However, you may "opam upgrade" these packages explicitly, which will ask permission to downgrade or uninstall the conflicting packages. Nothing to do.