13.18 The light of lights Krishna speaks

ज्योतिषामपि तज्ज्योतिस्तमसः परमुच्यते
ज्ञानं ज्ञेयं ज्ञानगम्यं हृदि सर्वस्य विष्ठितम्

jyotiṣhām api taj jyotis tamasaḥ param uchyate
jñānaṁ jñeyaṁ jñāna-gamyaṁ hṛidi sarvasya viṣhṭhitam

The light of lights, said to be beyond the dark; it is knowledge, what is to be known, and what knowledge reaches — seated in the heart of all.

Explanation

The light of lights, beyond the dark.

And then the collapse of the chapter's own three-part scheme: it is knowledge, and what is to be known, and what knowledge reaches. All three.

Arjuna asked for six definitions in 13.1. Here three of them turn out to name the same thing, seated in the heart of all.