Abstract:
It is described the class of evolutionary equations of the first order of divergent type for a vector field $a(x , t), x \in К:3бе\in R$, which are invariant relative to time $t \in R$ and spatial translations and which are covariant relative to all group $O_3$ transformations. Each equation of this class is fully characterized by a pair of differentiable functions f and g which are defined on $R^+$. In the class of equations found, the class of hyperbolic Friedrichs equations is distinguished. Each equation that is characterized by a pair of functions $f$ and $g$ belongs to this class if and only if the $f ' g > 0$ takes place.
