That's just silly, though. "tar" is pretty easy to use in its basic form, and I have dozens of commands ingrained in my memory.

    tar tf filename.tar
    tar xf filename.tar
    tar xfz filename.tar.gz   # Newer tars don't even require the z
    tar cfz filename.tar.gz directoryname

Heck, surely even

    tar --help

would suffice.

More interesting questions would be like: "which lower-case letters are NOT valid options to GNU ls". :)