xbasc()/// @@prerequisite 
a=get("current_axes");  /// \sleftarrow{\normalfont gets a handle on the newly created axes}
a.axes_visible="off";  /// \sleftarrow{\normalfont  makes the axes invisible}
a.data_bounds=[-2*cos(%pi/6),0;2*cos(%pi/6),3];  ///  \sleftarrow {\begin{minipage}[t]{4cm}{\nf{}sets the boundary values {for}\\ x and z }\end{minipage}}
a.box="off";
theta=[-%pi/6,%pi/2,%pi*7/6,-%pi/6];
T=[cos(theta);sin(theta)];
Ts=(1/(1+2*sin(%pi/6)))*rotate(T,%pi);
x=[T(1,:);Ts(1,:)]'; y=[T(2,:);Ts(2,:)]';
x=[x+cos(%pi/6),x-cos(%pi/6),x];
y=[y+sin(%pi/6),y+sin(%pi/6),y+1+2*sin(%pi/6)];
a.thickness=8;  /// \sleftarrow{\normalfont sets line thickness }\index{xset!thickness}
xpolys(x,y);  /// \sleftarrow{\normalfont draws a set of polylines (Figure~\ref{f:gr9})}\index{xpolys@\texttt{xpolys}}
xs2ps(0,'fig9');/// @@prerequisite affectations 
unix(SCI+'/bin/BEpsf fig9');/// @@prerequisite