OK so let me get this right. I type my script, it runs to say 100 A4 normal portrait sheets and to print it I choose bookfold layout on a duplex printer. When it prints out it will automatically change to say 50 landscape pages and numbered so that one side has two sets of columns numbered 1 and 4 and the other side will be 2 and 3. And that will be followed by subsequent pages with 5 and 8 on one side and 6 and 7 on the other side ad finitum until all the sheets print out.

I f that works it would be just what I want.