"संसार अस्थिर और क्षणिक है" यह कथन मूलतः किस दार्शनिक परम्परा से सम्बन्धित है?

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?