$obt(\overrightarrow{C}) \geq 1$. To show that $obt(\overrightarrow{C}) \le 1$, embed the vertices into the spine so that the spine order is a natural ordering of $V(\overrightarrow{C})$, say $\phi(1), \phi(2),..., \phi(n)$. Embed the arc $a$ with endpoints $\phi(1)$,$\phi(n)$ into the page. For $1 < i \le n-1$, embed every arc having the same direction as $a$ into the page and embed each arc having the opposite direction of $a$ into the spine. Thus we obtain a 1-page oriented book embedding, and $obt(\overrightarrow{C}) \le 1$. Since we have shown that $1 \le obt(\overrightarrow{C}) \le 1$, we conclude that $obt(\overrightarrow{C}) = 1$.

Oriented Trees
--------------

We now discuss oriented book embeddings of oriented trees and oriented forests, and introduce a type of oriented tree, called a [*fountain tree*]{}, which will be utilized in Section 4. A [*tree*]{}, denoted $T$, is a connected graph having no cycle as a subgraph. An [*oriented tree*]{}, denoted $\overrightarrow{T}$, is an oriented graph whose underlying graph is a tree.

The authors in [@SQLptI], focusing on oriented graphs which contain no directed cycle, use a restricted definition of oriented book embeddings, requiring the direction of all arcs in every page to agree and such that no arc is embedded 