When no case-ending follows (i.e. at the end of a word, in the narrower sense), r is substituted for the n of ahan,
Thus अहर्ददाति, अहर्भुङ्क्ते ॥ Why do we say 'when no case-ending follows'? Observe अहोभ्याम्, अहोभिः ॥ Here रु-called र् replaced the final न् of अहन् ॥ The difference between this रु-called र and the ordinary र is illustrated in the above set of examples. The रु-called र is changed to उ by 6.1.113, the ordinary र is not so changed.
Objection:- In अहर्ददाति and अहर्भुङ्क्ते the case-ending is elided after अहन्, and so by Pratyaya-lakshana, we may say that there is a case-ending here also ? Answer:- This is not so, because of the following maxim अहो रविधौ लुमता लुप्ते प्रत्यय लक्षणं न भवति ॥ The rule of pratya lakshana does not apply to the substitution of र for the final of अहन् when the affix has been elided by लुक् or लुप्. Therefore, this अहन् is not considered to be followed by सुप् or case-affix. But where an affix is elided by using the word लोप, there the rule of Pratyaya-lakshana does apply to अहन् ॥ As हे दीर्घाहोऽत्र, हे दीर्घाहो निदाघ. 8.2.7. Here the affix is elided by using the word 'lopa' by 6.1.68.,