(self)
Returns the index which is preferred to keep in the final expression.

        The preferred index is the index with more information regarding fermi
        level.  If indices contain same information, 'a' is preferred before
        'b'.

        Examples
        ========

        >>> from sympy.functions.special.tensor_functions import KroneckerDelta
        >>> from sympy import Symbol
        >>> a = Symbol('a', above_fermi=True)
        >>> i = Symbol('i', below_fermi=True)
        >>> j = Symbol('j', below_fermi=True)
        >>> p = Symbol('p')
        >>> KroneckerDelta(p, i).preferred_index
        i
        >>> KroneckerDelta(p, a).preferred_index
        a
        >>> KroneckerDelta(i, j).preferred_index
        i

        See Also
        ========

        killable_index
Returns the index which is preferred to keep in the final expression.
Returns the index which is preferred to keep in the final expression .
def preferred_index(self):
        """
        Returns the index which is preferred to keep in the final expression.

        The preferred index is the index with more information regarding fermi
        level.  If indices contain same information, 'a' is preferred before
        'b'.

        Examples
        ========

        >>> from sympy.functions.special.tensor_functions import KroneckerDelta
        >>> from sympy import Symbol
        >>> a = Symbol('a', above_fermi=True)
        >>> i = Symbol('i', below_fermi=True)
        >>> j = Symbol('j', below_fermi=True)
        >>> p = Symbol('p')
        >>> KroneckerDelta(p, i).preferred_index
        i
        >>> KroneckerDelta(p, a).preferred_index
        a
        >>> KroneckerDelta(i, j).preferred_index
        i

        See Also
        ========

        killable_index

        """
        if self._get_preferred_index():
            return self.args[1]
        else:
            return self.args[0]
def preferred_index ( self ) : if self . _get_preferred_index ( ) : return self . args [ 1 ] else : return self . args [ 0 ]