प्रगृह्य-सन्धि - 2

No सन्धि takes place when any vowel follows; in the following cases:

1. When the dual form of any noun/pronoun/verb ends in ई/ऊ/ए. E.g.1.कवी+एतौ=कवी एतौ। 2.माले+अमू=माले अमू। 3.वायू+इमौ=वायू इमौ।
2. When ई/ऊ follows म् of अदस् pronoun in its declension. E.g.1.अमी+ईशाः=अमी ईशाः। 2.अमू+आगते=अमू आगते।
3. When a single-vowel-particle :(except आ when it means 'a little, exclusive or inclusive' OR when आ is used as a preposition) is used.E.g. इ इन्द्र। (O इन्द्र!), उ उमेश। (O उमेश!), आ इदम्। (Ah, this!) but आ+उष्णम्=ओष्णम्। (a little warmth).
4. When an indeclinable ending in ओ is used.E.g. अहो उत्तमाः। The Vocative case-words optionally combine with इति. E.g.विष्णो+इति= विष्णो इति।OR विष्णविति। OR विष्ण इति।

The सन्धि is optional: When the particle उ is preceded by the consonants of the first 5 classes except ञ्, it is optionally changed to व्. E.g. किम्+उ+उक्तम्=किमु+उक्तम्= किम्वुक्तम्। OR किमु उक्तम्।(refer 3. above)