SYM.DSK is a special disk formatted for both NitrOS-9 and Disk Basic.

So, if you boot Disk Basic and have this dsk in drive0, you can RUN"SYM".
If you boot NitrOS-9 and have this disk in /D0, you can
load /d0/cmds/symmetry
and then enter
symmetry
Of course you could just
copy /D0/CMDS/symmetry /DD/CMDS/symmetry
and run it from your main drive.