./ivltests/sf_isunknown_fail.v:7: error: constant function $isunknown() does not support a string argument (1).
./ivltests/sf_isunknown_fail.v:8: error: constant function $isunknown() does not support two arguments.
ERROR: ./ivltests/sf_isunknown_fail.v:6: $isunknown's argument must be numeric.
ERROR: ./ivltests/sf_isunknown_fail.v:7: $isunknown's argument must be numeric.
ERROR: ./ivltests/sf_isunknown_fail.v:8: $isunknown takes a single numeric argument.
                                         Found 1 extra argument.