Pāṇini' rule "ग्रहोऽलिटि दीर्घ:" [७।२।३७] prescribes the lengthening of "i" in forms like गृहीत, गृहीत्वा etc.  Is there a historical explanation of this lengthening?

Madhav M. Deshpande
Professor Emeritus, Sanskrit and Linguistics
University of Michigan, Ann Arbor, Michigan, USA
Senior Fellow, Oxford Center for Hindu Studies
Adjunct Professor, National Institute of Advanced Studies, Bangalore, India

[Residence: Campbell, California, USA]