> $\xcancel{\begin{matrix}
a|bc \to \boxed{a}|bc \to ab|c\\
a|bc \leftarrow \boxed{a}b|c \leftarrow ab|c\\
c|ba \to c|b\boxed{a} \to cb|a
\end{matrix}}$
a|bc \to \boxed{a}|bc \to ab|c\\
a|bc \leftarrow \boxed{a}b|c \leftarrow ab|c\\
c|ba \to c|b\boxed{a} \to cb|a
\end{matrix}}$
