mapcons($f$;${\it as}$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$Case of ${\it as}$; nil $\rightarrow$ nil ; $a$.${\it as'}$, rec: $\rightarrow$ ($f$($a$,${\it as'}$)).mapcons($f$;${\it as'}$)
\\[0ex]\emph{(recursive)}