f,proofend=,for=size-lemma]{via induction over the depth $i$.}
      \begin{spfcases}{We have to consider two cases}
        \begin{spfcase}{$i=0$}
          \begin{spfstep}[display=flow]
            then $\livar{V}i=\set{\livar{v}r}$, where $\livar{v}r$ is the root, so
            $\eq{\card{\livar{V}0},\card{\set{\livar{v}r}},1,\power20}$.
          \end{spfstep}
        \end{spfcase}
        \begin{spfcase}{$i>0$}
          \begin{spfstep}[display=flow]
           then $\livar{V}{i-1}$ contains $\power2{