1. Tooling

The content of this paragraph consists of reminders of fundamental results, used in the following.

Special functions are, in general, constructed from the fundamental procedures of analysis: limit crossing in a finite sum of elements where the number of elements grows indefinitely, which gives series, and limit crossing in a finite product of elements, which gives infinite products. The integral is defined as the limit of a finite sum, but this is a more complex process; Riemann integral theory is assumed.