\begin{tabbing}
ecl{-}base{-}tuple($k$; ${\it test}$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=$<\mathbb{B}$\+
\\[0ex], cons($k$; [])
\\[0ex], ff
\\[0ex], $\lambda$${\it k'}$,$s$,$v$,$x$. bor(band(eq\_knd(${\it k'}$; $k$); (${\it test}$($s$,$v$))); $x$)
\\[0ex], $\lambda$$n$,$x$. band($x$; ($n$ =$_{0}$ 0))
\\[0ex], $\lambda$$n$,${\it k'}$,$s$,$v$,$x$. ff
\\[0ex], []$>$
\-
\end{tabbing}