Reduplication is the unique prefix given to perfect tense verbs in Greek. cf. vocalic reduplication.
If a verb begins with a single consonant, that consonant is reduplicated and the two consonants are separated by an epsilon.
λυω (present tense) becomes λελυκα (perfect tense).
ποιεω (present tense) becomes πεποιηκεν (perfect tense).
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If the consonant that was reduplicated is φ, χ, or θ then the reduplicated consonant will change to π,κ, or τ respectively. cf. BBG 25.8.
φανεροω (present tense) becomes πεφανερωκα (perfect tense)
τιθημι (present tense) becomes τέθειται (perfect tense).
