肇論新疏 2.209

2.209

是以辨同者同於異，辨異者異於同（三、俱句），斯則不可得而異、不可得而同也（四、非句）。

Therefore, discerning identity means being identical in difference; discerning difference means being different in identity (the third, both-clause). Thus they cannot be made to be different, nor can they be made to be identical (the fourth, neither-clause).