[woko]

This quote is specifically about Diophantine equations.

You can find a similar statement as "Proposition 3.2.2" in Chapter 3 "Modular Arithmetic" [1] of this introductory course [2] to Number Theory. Here is a picture of the statement [3].

Basically, if there exists a number n such that there is no solution modulo n, then you know there are no solutions. Here is a simple application [4] of the proposition with n = 2 and 3.

[1] <http://www2.math.ou.edu/~kmartin/intro-nt/ch3.pdf> [2] <http://www2.math.ou.edu/~kmartin/intro-nt/>

[3] <https://i.ibb.co/8mNHW0Q/2021-09-20-10-34-25.png> [4] <https://i.ibb.co/Qffr9k2/2021-09-20-10-56-29.png>