i is substituted for the final short a of the reduplicate in the Desiderative.,
As पिपक्षति, यियक्षति, 8.2.36, 8.2.41 तिष्ठासति, पिपासति ॥ Why do we say in the Desiderative? Observe पपाच ॥ Why do we say \for the अ\? Observe लुलूषति ॥ Why do we say 'short अ'? Observe पापचिषते the Desiderative of the Intensive पापच्यते ॥,