assuming the conversion of āy in both alike—but probably only as a matter of formal convenience in rule-making.
b. Here, too (as in the similar cases of e and āi and o: 133 c, 176b), there are examples to be found, both earlier and later, of effacement of the hiatus.
178. Final र् r, in general, shows the same form which स् s would show under the same conditions.
a. Thus, it becomes visarga when final, and a sibilant or visarga before an initial surd mute or sibilant (170): thus, rudatī punaḥ, dvās tat, svàç ca, catúçcatvāriṅçat; and (111c, d) prātastána, antastya, catuṣṭaya, dhūstva; prātaḥ karoti, antaḥpāta.
b. But original final r preceded by a or ā maintains itself unchanged before a sonant: thus, punar eti, prātarjit, ákar jyótiḥ, áhār dā́mnā, vārdhi.
c. The r is preserved unchanged even before a surd in a number of Vedic compounds: thus, aharpáti; svàrcanas, svàrcakṣas, svàrpati, svarṣā́, svàrṣāti; dhūrṣád, dhūrṣah; pū́rpati, vārkāryá, āçī́rpada, punartta; and in some of these the r is optionally retained in the later language. The RV. also has āvar támaḥ once in sentence-combination.
d. On the other hand, final ar of the verb-form āvar is changed to o before a sonant in several cases in RV. And r is lost, like s, in one or two cases in the same text: thus, akṣā índuḥ, áha evá.
179. 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.
180. The dental sibilant स् s is changed to the lingual ष् ṣ, if immediately preceded by any vowel save अ a and आ ā, or by क् k or र् r—unless the स् s be final, or followed by र् r.
a. The assimilating influence of the preceding lingual vowels and semivowel is obvious enough; that of k and the other vowels appears to be due to a somewhat retracted position of the tongue in the mouth during