The augments come after the reduplicate of a root which has ṛ at the penultimate position, only when the yaṅ of the Intensive is elided.,
Thus नर्नत्ति, नरिनर्ति, and नरीनर्ति; वर्वर्ति, वरिवर्ति, वरीवर्ति ॥ The उ in रुक् is for the sake of pronunciation, the augment is र् ॥
Vart:- मर्मृज्यते and मर्मृज्यमानासः should also be enumerated. These have taken रुक् augment, though the यङ् is not elided here.,