khyāñ is optionally the substitute of cakṣiṅ when liṭ (Perfect Tense) follows.,
The लिट् also is an ardhadhatuka affix and by the last sutra ख्या would always have been the substitute of चक्ष्; the present sutra makes this substitution optional, as आचख्यौ, आचख्यतुः and आचख्युः. In the alterative we have आचचक्षे, आचचक्षाते and आचचक्षिरे 'he told &c.',