Commodities and Prices

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'.

Mathematics

...the sets which constitutes the universe of discourse must always be explicitly listed at the outset...

This is like the notes made when reading mathematics by someone who is trying to figure out the link between the mathematical wisdom and his own problems in mind.
Tuples are ordered sets, sets the order of whose elements are essential, thus containing an additional dimension of information.
The graph of a function is also a set, only with a correspondence in between its elements.
A projection is a function assciating a point (graph) with its coordinates, while the association of a coordinate to a point (graph) containing it is also a function. These functions differ from the other ones in that