[ false 0 rot
    witheach
      [ i + bit
        2dup & iff
          [ drop dip not
            conclude ]
          done
        | ]
    drop ]               is l-bishop ( [ --> b )

  [ reverse l-bishop ]   is r-bishop ( [ --> b )

  [ [] swap perms
    witheach
      [ dup l-bishop iff
          drop done
        dup r-bishop iff
          drop done
        nested join ] ]  is queens   ( n --> [ )

  8 queens
  dup size echo say " solutions."
  cr cr
  witheach
    [ echo
      i^ 1+ 4 mod iff sp else cr ]