def subtract(datae):
 """Subtracts two fields
 
 Parameters
 ----------
 
 datae    : list
            List of `np.ndarray` with the fields on which the function operates.
 
 Returns
 -------
 
 numpy.ndarray
            Subtracts the second field to the first field in `datae`. Thought to
            process a list of two fields.
 
 """
 return datae[0] - datae[1]