  The sets of vertices and edges of an undirected, simple, finite, connected
graph $G$ are denoted by $V(G)$ and $E(G)$, respectively. An arbitrary nonempty
finite subset of consecutive integers is called an interval. An injective
mapping $\varphi:E(G)\rightarrow \{1,2,...,|E(G)|\}$ is called a labeling of
the graph $G$. If $G$ is a graph, $x$ is its arbitrary vertex, and $\varphi$ is
its arbitrary labeling, then the set $S_G(x,\varphi)\equiv\{\varphi(e)/ e\in
E(G), e \textrm{is incident with} x$\} is called a spectrum of the vertex $x$
of the graph $G$ at its labeling $\varphi$. For any graph $G$ and its arbitrary
labeling $\varphi$, a structure of the subgraph of $G$, induced by the subset
of vertices of $G$ with an interval spectrum, is described.
