How To Access Server Variable In Aspx

I've defined a session variable in my Session_Start procedure

void Session_Start(object sender, EventArgs e)
{
<other stuff>
string sAdmin= bAdmin.ToString();
Session["SessionAdmin"] = sAdmin;
}

Then in my masterpage I want to use the Session Variable to conditionally show some links in a list.

How do I write the Boolean expression to correctly access the session variable SessionAdmin?

Here's what I have:

<div id="menu">
<ul>
<li><a href="/EmployeeTime.aspx">Employee Time</a></li>
<% if ( *** a Boolean expression involving Session variable "SessionAdmin" *** ) {%>
<li><a href="/Employee.aspx">Employees</a></li>
<li><a href="/ProductLine.aspx">Product Lines</a></li>
<li><a href="/Task.aspx">Tasks</a></li>
<li><a href="/Type.aspx">Work Types</a></li>
<li><a href="/Activity.aspx">Activities</a></li>
<%} %>>
</ul>
</div>

How do I correctly define my boolean expression? I've been looking, but haven't found the right syntax.