countable{-}p{-}union($i$.$A$($i$))($p$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$if ($p$.1 =$_{0}$ 0) then 0 else imax{-}list(map($\lambda$$i$.$A$($i$)($p$);upto($p$.1))) fi