The stem of the first perfect is formed by adding -κα to the reduplicated verb-stem. λέ-λυ-κα
a. The κ-perfect is later in origin than the second perfect and seems to have started from verb-stems in -κ, as ἔ-οικ-α (= ϝέ-ϝοικ-α) from εἴκω
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].