179. A double r

A double r is nowhere admitted: if such would occur, either by retention of an original r or by conversion of s to r, one r is omitted, and the preceding vowel, if short, is made long by compensation.

Thus, punā ramate, nṛpatī rājati, mātū́ rihán, jyotīratha, dūrohaṇá.

a. In some Vedic texts, however, there are instances of ar changed to o before initial r: thus, svò rohāva.