\begin{tabbing}
es{-}next{-}bool{-}assign\=\{i:l\}\+
\\[0ex](${\it es}$; $x$; $b$; $e$; ${\it bound}$)
\-\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$es{-}next{-}assign\=\{i:l\}\+
\\[0ex](${\it es}$; $\mathbb{B}$; BoolDeq; $b$; $x$; $e$; ${\it bound}$)
\-
\end{tabbing}