{ 'c', 'i', 'o', 'p' }

##</code><code>##

    S   ->  Sp
    op  ->  i
    ip  ->  c
    oc  ->  io
    ic  ->  co
    cS  ->  ioS

##</code><code>##

    $S = 'o';
    
    for (1..16) {
        $S .= 'p';                  # S  -> Sp
        @processing = ($S);
    
        $S =~ s/op/i/;              # op -> i
        $S =~ s/ip/c/;              # ip -> c
        push @processing, $S;
    
        while ($S =~ /c/) {
            $S =~ s/oc/io/;         # oc -> io
            $S =~ s/ic/co/;         # ic -> co
            $S =~ s/^c/io/;         # cS -> ioS
            push @processing, $S;
        }
        
        @out = map { sprintf ("%6s", $_) } @processing;
        printf ("%-44s == %6s\n", join (" ->", @out), $S);
    }

##</code><code>##

        op ->     i                              ==      i
        ip ->     c ->    io                     ==     io
       iop ->    ii                              ==     ii
       iip ->    ic ->   ioo                     ==    ioo
      ioop ->   ioi                              ==    ioi
      ioip ->   ioc ->   iio                     ==    iio
      iiop ->   iii                              ==    iii
      iiip ->   iic ->   ico ->  iooo            ==   iooo
     iooop ->  iooi                              ==   iooi
     iooip ->  iooc ->  ioio                     ==   ioio
     ioiop ->  ioii                              ==   ioii
     ioiip ->  ioic ->  ioco ->  iioo            ==   iioo
     iioop ->  iioi                              ==   iioi
     iioip ->  iioc ->  iiio                     ==   iiio
     iiiop ->  iiii                              ==   iiii
     iiiip ->  iiic ->  iico ->  icoo -> ioooo   ==  ioooo

##</code><code>##

    $S = 'opppppppp';               # (S  -> Sp) x 8
    
    while ($S =~ /p/) {
        @processing = ($S);
        
        $S =~ s/op/i/;              # op -> i
        push @process, $S;
        $S =~ s/ip/c/;              # ip -> c
        push @processing, $S;
    
        while ($S =~ /c/) {
            $S =~ s/oc/io/;         # oc -> io
            $S =~ s/ic/co/;         # ic -> co
            $S =~ s/^c/io/;         # cS -> ioS
            push @processing, $S;
        }
        
        @out = map { sprintf ("%9s", $_) } @processing;
        print join (" ->", @out), "\n";
    }

##</code><code>##

    opppppppp -> ippppppp ->  cpppppp -> iopppppp
     iopppppp ->  iippppp ->   icpppp ->  ioopppp
      ioopppp ->   ioippp ->    iocpp ->    iiopp
        iiopp ->     iiip ->      iic ->      ico ->     iooo

##</code><code>##

    8   ->  iooo