首楞嚴義疏注經 6.220

6.220

阿那律陀因修樂見照明三昧，旋見循元，由斯得證。今云見性雖有洞然照了之義，而又前方全明，後方全暗，左右傍觀三分之二，故云四維虧一半也。

Aniruddha, by cultivating the samādhi of joyful seeing and luminous illumination, reversed seeing to follow the origin, and through this attained realization. Here it is said: although the seeing-nature has the quality of penetrating illumination, the front is completely bright while the rear is completely dark, and looking sideways to the left and right covers two-thirds; therefore it says that 'the four corners lack by half'.