Introduction
Many Americans remember a horrible and sorrowful day of December, 14, 2012, when 26 people, including 20 students, were shot to death at the Sandy Hook Elementary School in Newtown, Connecticut (7). After that, the USA has seen an awful string of new gun massacres, and question of control of gun ownership and usage had become acute as never before this. It’s well-known, that in some states a teenager requires parental permission to play in a sports team, but not to own a shortgun. In many states, the number of firearms owned by one person is not limited (1). The rate ...