मथुरा कला में, नातेदारी त्रय (kinship triads) को दर्शाने वाली मूर्तियाँ किन देवताओं को निरूपित करती हैं?

In Ancient Indian Statecraft, Kautilya's 'Rajamandala' theory primarily deals with:

The First Buddhist Council was held at ______.

Which ancient Indian text contains references indicating that population counts or census-like records were maintained in ancient India?