debugged.

dbg$psp
    (DOS only) This debugger symbol contains the segment value for the DOS
    "program segment prefix" of the program being debugged.

dbg$radix
    This debugger symbol represents the current default numeric radix.

dbg$remote
    This debugger symbol is 1 if the "REMotefiles" option was specified and
    0 otherwise.

dbg$sp
    This debugger symbol represents the register pair SS:SP (16-bit mode) or
    SS:ESP (32-bit mode).

    Example:

         ? dbg$sp


dbg$loaded
    This debugger symbol is 1 if a program is loaded.  Otherwise, it is 0.

dbg$nil
    This debugger symbol is the null pointer value.

dbg$src
    This debugger symbol is 1 if you are currently debugging in an area that
    contains debugging information.