[In traditional grammars durative is named "present", durative past indicative "imperfect"]

9. [--ν-αν-] This category , to which some very important verbs belong, produces lots of forms that not easily found by way of the dictionary:
who would for example look under
λαμβάνω when analyzing ἔλαβε?

ἁνδάνω, ἁδ(η)-

θιγγάνω, θιγ-, τιγ-

λαγχάνω, λαχ-, (εἰ)ληχ-

λαμβάνω, λαβ-, (εἰ)ληβ-, λαβη-

λανθάνω, λαθ-, (εἰ)ληθ-

μανθάνω, μαθ(η)-

πυνθάνομαι, πευθ-, πυθ-

τυγχάνω, τυχ(η)-, τευχ-

χανδάνω, χαδ-, χαν(δ)-, χονδ-

The stem-variants εἰληχ-, εἰληβ-, εἰληθ- are reduplication-inclusive (εἰληχ- <εἱληχ- <σεσληχ- etc.), and therefore occur only in perfect forms.