[Groff] pic: xslanted/yslanted not recognized

[Larry Kollar]

Minimal example:

        .PS
        box xslanted 0.1 yslanted 0.5;
        .PE

        % groff -ms -p junk.pic > junk.ps
        pic:junk.pic:2: there is no variable `xslanted'
        pic:junk.pic:2: giving up on this picture
        %

Am I doing this wrong?

-- Larry