Reducible (control) flow graph

Reducible (control) flow graph --- сводимый управляющий граф.

Let $G$ be a cf-graph and let $k\geq 0$. The $k$derived cf-graph $G_k$ of $G$, denoted $G_k=I_k(G)$, is defined by the following rules: $G_0=G$, and for any $k>0$ the cf-graph $G_k$ is derived from the cf-graph $G_{k-1}$ by reduction of its maximal interval into nodes. The limit cf-graph of $G$ is defined as its $k$-derived cf-graph $G_k$ such that $G_k=I_{k+1}(G)$. $G$ is called (interval) reducible if its limit cf-graph is trivial and (interval) irreducible otherwise.