/frames 14 def /figflag 1 def

%include /u/rs/book3/pslib/tools.ps
%include /u/rs/book3/pslib/example.ps

/partition
 { 
   /r exch def /l exch def
   /v A r get def
   /j r def /i l 1 sub def
   l r SUBFILE
   r frame 1 add PTmark nextframe
   {
     /oldi i def /oldj j def
     { /i i 1 add def A i get v ge { exit } if } loop
     oldi 1 add i SUBFILE
     { /j j 1 sub def A j get v le { exit } if } loop
     j oldj 1 sub SUBFILE
     j i lt { exit } if
     j i swap
     l i j r SUBFILEtwo nextframe
   } loop
   i r swap nextframe
   l r SUBFILE
   i frame 1 add PTmark
 } def

LL RR partition
--------------------
T 10.25pc Partitioning example

Quicksort partitioning begins by choosing a partitioning element, in
this case the rightmost element, the {\F E}. Then the process involves
scanning from the left, stopping at larger elements, and from the
right, stopping at smaller elements.  First, the scan from the left
stops at the {\F S}, then the scan from the right stops at the {\F A},
and then these two are exchanged.  Next, the scan from the left stops
at the {\F O}, then the scan from the right stops at the {\F E}, and
then these two are exchanged.  Next, the pointers cross.  The scan
from the left stops at the R, and the scan from the right stops at the
{\F E}.  To finish the process, the paritioning element (the {\F E} at
the right) is exchanged with the {\F R}.