[NTG-context] cutting pages for booklet

Dear list, the way to have a booklet is straightforward: \setuppapersize[A4][A3, landscape] \setuparranging[2UP] \setupbodyfont[128pt] \setupmakeup[page] [pagestate=start, align=center, style=\ssbfd] \starttext \dorecurse{24} {\startmakeup[page]\recurselevel\stopmakeup} \stoptext But what happens if I already have landscape A3 that I need to print as an A4 booklet? I mean, which is the way to instruct ConTeXt to cut each A3 page in half and arrange each half in its proper position in the booklet? Many thanks for your help, Pablo