Since Germanic has -e:(i) in verbs corresponding with BS
-êti, perhaps a solution along the lines of Jens' soundlaws
for "long diphthongs" can be envisaged:
*-éh1i- gives -é: in the 3rd. aorist *-éh1i-t > *-éh1-t,
whence the infinitive system.
In the present, stressed full-grade *-éh1i- + vowel gives
*-é:i- > *-éi- > Slavic -í:-, and *-éh1i- + single consonant
gives *-eiH- > *-éi- and also Slavic -í:-.
Unstressed zero-grade *-h1i- + vowel or voiced consonant
gives Lith. -i-.
=======================
Miguel Carrasquer Vidal
mcv@...