Example 1 (block)#
$$
a^*=x-b^*
$$
Example 2 (block)#
$$
\begin{array} {lcl}
L(p,w_i) &=& \dfrac{1}{N}\Sigma_{i=1}^N(\underbrace{f_r(x_2
\rightarrow x_1
\rightarrow x_0)G(x_1
\longleftrightarrow x_2)f_r(x_3
\rightarrow x_2
\rightarrow x_1)}_{sample\, radiance\, evaluation\, in\, stage2}
\\\\\\ &=&
\prod_{i=3}^{k-1}(\underbrace{\dfrac{f_r(x_{i+1}
\rightarrow x_i
\rightarrow x_{i-1})G(x_i
\longleftrightarrow x_{i-1})}{p_a(x_{i-1})}}_{stored\,in\,vertex\, during\,light\, path\, tracing\, in\, stage1})\dfrac{G(x_k
\longleftrightarrow x_{k-1})L_e(x_k
\rightarrow x_{k-1})}{p_a(x_{k-1})p_a(x_k)})
\end{array}
$$