EXCEPTIONS OF वृद्धि-सन्धि - 1

In the following cases, instead of the substitution of वृद्धि vowels in place of गुण vowels occurring after अ/आ, गुण vowels are only substituted.

• When an उपसर्ग ending in अ/आ is used before a root beginning with ए/ओ. However, for the denominative root, this गुण is optional.
  E.g. प्र + एजते = प्रेजते, प्र + ओषति = प्रोषति । However, उप + एडकीयति = उपेडकीयति or उपैडकीयति ; and उप + ओघीयति = उपोघीयति or उपौघीयति ।
  COUNTER EXCEPTION wherein वृद्धि is only substituted:-
  A.When an उपसर्ग ending in अ/आ is used before एति (from root "इ - 2 प.") and एधति (from root "एध् - 1 आ.") where the form of the root has an initial ए. E.g. उप + एति = उपैति, (but अव + एहि = अव + आ + इहि = अवेहि - because here 'इहि' does not have an initial ए by itself) । उप + एधति = उपैधति ।B.When प्र is used before एष, एष्य (from root इष् - 4 प., 6 प. and 9 प.). E.g. प्रैषः , प्रैष्यः (but प्रेषः ; derived from root ईष् and not इष्) ।