A proof tree for the statement “$(0+1)(0+1) \matches 10$”:
\[ \begin{prooftree} \AxiomC{} \LeftLabel{$\rlnm{Char}$} \UnaryInfC{$1 \matches 1$} \LeftLabel{$\rlnm{ChoiceR}$} \UnaryInfC{$0+1 \matches 1$} \AxiomC{} \LeftLabel{$\rlnm{Char}$} \UnaryInfC{$0 \matches 0$} \LeftLabel{$\rlnm{ChoiceL}$} \UnaryInfC{$0+1 \matches 0$} \LeftLabel{$\rlnm{Concat}$} \BinaryInfC{$(0+1)(0+1) \matches 10$} \end{prooftree} \]