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.