Interests and exchange rates are prices with time and location, in addition to value, specified of a commodity. From Debrau's interpretation of time and space as consisted of elementary intervals, a connection with the language of calculus is suggested. A commodity was specified in a 'brute-force' manner. It was defined as what it consists of, a good or a service, but there isn't a more general and fundational definition. It is not clear whether it can be defined as something for exchange, highlighting the essence of what it means to be 'economic'.