In the room of e or o final in a pada , and the short a , which follows it, is substituted the single vowel of the form of the first (e or o),
Thus अग्ने + अत्र = अग्नेऽत्र, वायो + अत्र = वायोऽत्र ॥ This supersedes the substitutes अय् and अव् ॥ Why do we say 'of ए or ओ'? Observe दध्यत्र, मध्यत्र ॥ Why do we say 'final in a Pada'? Observe चे + अन = चयनम्, लो + अन = लवनम् ॥ Here the ए or ओ are in the body of the word, and not at the end of a word. Why do we say \when followed by a short अ\? Observe वायो + इति = वायविति, भानो + इति = भानविति ॥ Why do we say 'short'? Observe वायो आयाहि = वायवायाहि ॥,