  The article discusses the representation of discrete functions defined in an
analytic form without the use of approximations, namely the Heaviside function,
identity function, the Dirac delta function and the prime-counting function.
Also in the article introduced and considered a new type of sets ($\xi$ set) by
analogy taken from finding the sum of a number of grants and other
contradictions in mathematics and physics. With the help of $\xi$ sets
interpreted Russell's paradox in the system of axioms of naive set theory.
