code: def na_cmp():
      def cmp(a, b):
          return np.isnan(a) and np.isnan(b)
  
      return cmp
  
imports: import numpy
  import pytest
  from pandas.core.dtypes.dtypes import NumpyEADtype
  import pandas
  import pandas._testing
  from pandas.api.types import is_object_dtype
  from pandas.core.arrays.numpy_ import NumpyExtensionArray
  from pandas.tests.extension import base
label_desc: Use image node_id 6 for calling a global function with example usage: na_cmp() and returns: cmp, unknown