na is substituted, at the end of a word, for the final ma of a root.,
As प्रशान्, प्रतान्, प्रदान् ॥ These are formed by adding क्विप् to the roots शम्, तम् and दम् ॥ The lengthening takes place by 6.4.15. The न् being considered as asiddha is not elided.
Why do we say \of म-ending roots\? Observe भित्, छित् ॥
Why do we say \of a root\? Observe इदम्, किम् ॥
The word पदस्य is understood here also. So we have प्रतामौ, प्रतामः where म is not at the end of a word.,