A long vowel is substituted in the reduplicate of the root i (eti) before a personal ending of the liṭ (Perfect Tense), which has an indicatory k,
As ईयतुः, ईयुः ॥ These are thus formed इ + अतुस् = य् + अतुः (य् substituted by इ 6.4.81). Then there is reduplication, the य् becomes sthanivat to इ by (I. I. 59), and we have इ य् + अतुः and then by the present rule इयतुः ॥ Why do we say before a कित् affix? Observe इयाय, इययिथ ॥,