*"There's no sense in being precise when you don't even know what you're talking about." (John von Neumann)*

## Prologue

For the typical primary school or high school student, the following definition of mathematics would suffice:

**(Naive definition)** Starting from obviously true axioms, use obviously correct inference rules to derive additional truths.

In this sense, mathematics is all about discovering indisputable truths. For example, the theorems proved in geometry would be literally true statements about the physical space. Someone may argue that there is no such physical object as a geometrical point, or a geometrical line, but this is no issue because we can reply that geometrical objects are nothing more than locations in the physical space, and thus they can happily exist even if nobody can see them materialized. As for the exotic topic of complex numbers, they can be viewed as a man-made tool that sometimes comes in handy for mathematicians in describing reality.Continue reading