def gradients_X(self, dL_dK, X, X2):
        raise NotImplementedError
we expect a STRING " " (NIL | STRING) pair.
dataset/ETHPy150Open SheffieldML/GPy/GPy/kern/src/kern.py/Kern.gradients_X--crossover with--dataset/ETHPy150Open scanner/asimap/asimap/parse.py/IMAPClientCommand._p_string_nstring_pairs