# Fragment

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Fragment --- фрагмент.

A subgraph of a control flow graph $G$ is called a fragment.

A fragment $A$ is a subfragment of $B$, if $A\subseteq B$; it is a proper subfragment if $A\neq B$.

A node $p$ of a fragment $A$ is called initial (respectively, output or exit) if either $p$ is the initial node of $G$ (respectively, $p$ is the terminal node of $G$) or an arc of $G$ not belonging to $A$ enters $p$ ( respectively, leaves $P$).

A node $p$ of a fragment $A$ is called its entry if there is a part from the initial node of $G$ to $p$ that includes no arcs of the fragment $A$. $p$ is called a terminal node of a fragment $A$ if $p$ does not belong to $A$ and is a successor of a node of $A$.

A node $p$ of a fragment $A$ other than the initial and terminal nodes of $G$ is called a boundary of $A$ if $p$ is the initial or output node of $A$.

Let $p$ be a boundary node of a fragment $A$. It is called starting of $A$ if $A$ contains no predecessors of $p$ or all successors of $p$. It is called finishingof $A$ if $A$ contains all predecessors of $p$ or no successors of $p$.