% Figure 2.2 begins

\def\vcut{\smash{\hbox to 20pt{\hss%
\hbox to 0pt{\hidewidth%
\vrule height20pt depth20pt width0.1pt%
\hidewidth}%
\hskip 10pt%
\hss}}}
												
\def\vxcut{\smash{\hbox to 20pt{\hss%
\hbox to 0pt{\hidewidth%
\vrule height20pt depth20pt width0.1pt%
\hidewidth}%
\hbox to 0pt{\hidewidth%
$\scriptstyle x + 4 \leftrightarrow x$%
\hglue 9pt\hidewidth}%
\hskip 10pt%
\hss}}}
												

\midinsert
\medskip

\centerline{
\vbox{\offinterlineskip
\setbox0=\hbox{\vt \ctright \vt \ctright \vt \hedg \vt \hedg \vt \hedg \vt}
\hsize=\wd0
\box0
\hbox{\ctup \phe \pvt \vxcut \chup \phe \pvt \phe \pvt \phe \vedg}
\hbox{\vt \phe \vt \hedg \vt \phe \vt \phe \vt \phe \vt}
\hbox{\ctup \phe \vedg \phe \ctup \phe \pvt \phe \pvt \phe \vedg}
\hbox{\vt \phe \vt \hedg \vt \phe \vt \hedg \vt \phe \vt}
\hbox{\hbox to 0pt{\hss \hidewidth $\xi_1$\ }%
\ctup \phe \pvt \phe \hbox to 0pt{\hss \hidewidth $\xi_2$\ }%
\chup \phe \vedg \phe \vedg \phe \vedg}
\hbox{\vt \phe \vt \phe \vt \phe \vt \hedg \vt \phe \vt}
\hbox{\ctup \phe \pvt \phe \chup \phe \pvt \vxcut \pvt \phe \vedg}
\hbox{\vt \ctright \vt \ctright \vt \hedg \vt \hedg \vt \hedg \vt}
\smallskip
\centerline{\strut(a)}
}
}
\vglue 20pt plus 20pt
\centerline{
\hglue 30pt plus \hsize
\vbox{\offinterlineskip
\setbox0=%
\hbox{\vti{0} \hedg \vti{1} \hedg \vti{-4}
\hedg \vti{-3} \hedg \vti{-4} \hedg \vti{-3}}
\hsize=\wd0
\box0
\hbox{\vedg \phe \pvt \vcut \vtedg \phe \vtedg \phe \pvt \phe \vedg}
\hbox{\vti{-1} \htedg \vti{-2} \hedg \vti{-5}
\phe \vti{-2} \htedg \vti{-1} \htedg \vti{-2}}
\hbox{\vedg \phe \vedg \phe \vedg \phe \vtedg \phe \pvt \phe \vedg}
\hbox{\vti{0} \phe \vti{-3} \hedg \vti{-4}
\htedg \vti{-3} \hedg \vti{-4} \htedg \vti{-3}}
\hbox{\vedg \phe \vtedg \phe \pvt \phe \vedg \phe \vedg \phe \vedg}
\hbox{\vti{-1} \htedg \vti{-2} \htedg \vti{-1}
\htedg \vti{-2} \hedg \vti{-5} \phe \vti{-2}}
\hbox{\vedg \phe \pvt \phe \vtedg \phe \pvt \vcut \vtedg \phe \vedg}
\hbox{\vti{0} \hedg \vti{1} \hedg \vti{0}
\hedg \vti{1} \hedg \vti{-4} \hedg \vti{-3}}
\smallskip
\centerline{\strut(b)}
}
\hskip 30pt minus 20pt
\vbox{\offinterlineskip
\setbox0=%
\hbox{\vti{0} \hedg \vti{1} \hedg \vti{0}
\hedg \vti{1} \hedg \vti{4} \hedg \vti{5}}
\hsize=\wd0
\box0
\hbox{\vedg \phe \pvt \phe \vtedg \phe \vtedg \vcut \pvt \phe \vedg}
\hbox{\vti{-1} \htedg \vti{-2} \hedg \vti{-1}
\phe \vti{2} \htedg \vti{7} \htedg \vti{6}}
\hbox{\vedg \phe \vedg \phe \vedg \phe \vtedg \vcut \pvt \phe \vedg}
\hbox{\vti{0} \phe \vti{-3} \hedg \vti{0}
\htedg \vti{1} \hedg \vti{4} \htedg \vti{5}}
\hbox{\vedg \phe \vtedg \vcut \pvt \phe \vedg \phe \vedg \phe \vedg}
\hbox{\vti{-1} \htedg \vti{-2} \htedg \vti{3}
\htedg \vti{2} \hedg \vti{3} \phe \vti{6}}
\hbox{\vedg \phe \pvt \vcut \vtedg \phe \pvt \phe \vtedg \phe \vedg}
\hbox{\vti{0} \hedg \vti{1} \hedg \vti{4}
\hedg \vti{5} \hedg \vti{4} \hedg \vti{5}}
\smallskip
\centerline{\strut(c)}
}
\hglue 30pt plus \hsize
}

\nobreak
\smallskip
\nobreak

\centerline{\bf Figure 2.2}
\smallskip
\endinsert

% Figure 2.2 ends
