letter following the root vowel, or diphthong, in the 1st pers. sing.
Pres. Indic. act., lexicon form: in "liquid" verbs (not derivatives in
άνω, which is merely strengthened for άω) this is a
_liquid_; in "pure" verbs it is absent, so that the root appears
to end in a vowel, etc. Very many verbs seem to be anomalous in some
of their forms in consequence of deriving these from an obsolete
kindred root. The lexicon gives most of these peculiarities.

§ 63. _Liquid_ verbs almost always strengthen their root in the
Pres. and Imperf.; they lengthen it in the 1st Aor. act. and mid. by
changing the root vowel, if α into η, if ε into ει, while ι and
ν merely become long. ε as a root vowel is generally changed into α
in the 1st Aor. and 1st Fut. pass., the Perf. and Pluperf. act. and
pass., and the 2d Aor. and 2d Fut. throughout, and again into ο in
the Perf. and Pluperf. mid.

§ 64. The above strengthening in the Pres. and Imperf. consists in
doubling λ, annexing ν to μ; or, in case of ν or ρ, in adding ι
to a preceding α or ε, or lengthening ι or υ. The radical ν is
often dropped in Perf. and Pluperf.

§ 65. Verbs with ε followed by a pi- or kappa-mute in the root
frequently neglect to strengthen it in the Pres. and Imperf.; and
verbs with ε in the root preceded by a liquid, usually change it into
α and ο in the same tenses as liquid verbs, except in the 1st
Aor. and Fut. pass.

§ 66. _Pure_ verbs lengthen the root vowel before a tense
characteristic, also in the Perf. and Pluperf. pass. A few
occasionally neglect this, and some insert σ instead.