Features of computer language: communication of computers and its complexity

Motivated by computer science, in particular, by applications to data security, electronic correspondence and cryptography, interactive proofs extend the 2000 years old, well established notion of mathematical proof. The key to these development is complexity which is defined as the minimum amount of a certain resource needed to complete a computational task. In this paper, the idea of an interactive proof system and its application in computer science is illuminated on everyday examples, without giving technical details.