 ${\mathcal{G}}(S {{\tikz[baseline=-0]{\draw (0,0) node[circle,fill=black,minimum size=0,inner sep=0]{} -- (0.0,0) node[circle,fill=black, minimum size=0, inner sep=0] {} node[midway,above,scale=0.0] {$0$};}}}S')=0$.  