\begin{figure}
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% diagram (a)
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%
%
% diagram (b)
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\end{picture}
\caption{(a) 
The order $\ac^2$ diagram peculiar to the axial
vector current correlator and leading to  to a singlet contribution
\protect \r{Kuhn:I_2over3} to $\G^A(Z\to \ovl b b)$;
(b) The lowest order diagram contributing to  the anomalous dimension
$\g^\psi$ and to the coefficient function ${\bf C}_h$ ;
(c) A lowest order diagram contributing to the coefficient function
${\bf C}_\psi$.
}
\label{fig1}
%
\end{figure}