Accepts strings of the form xww^ry, where |x| >= |y|.  The input alphabet is
{a,b}.

Method:  Find the middle of the string, then move right looking for
pairs of the form aa or bb (!).  We find the middle of the string by
alternately marking a's and b's on the left and on the right until the
two sequence of markings meet in the middle

--------------------------------------------------

(0ax1r      state 0:  left side of the a,b string is marked 
(0by1r      state 1:  move to right end of the a,b string
(1aa1r
(1bb1r

(1  2l      state 2:  found the right end of the a,b string,
(1xx2l                   mark of the rightmost a or b.
(1yy2l

(2ax3l      state 3:  move to left end of the a,b string.
(2by3l

(3aa3l
(3bb3l
(3xx0r        found the left end of the a,b string.  Go back to state 0
(3yy0r

(0xx4r        no more a's or b's left to mark.
(0yy4r
(2xx4r
(2yy4r
        State 4:
The a,b string is completely marked.  We are at the middle of the string.
Now go right looking for aa or bb pair, namely, an xx or yy pair...

(4xx5r  state 4:  read a first symbol 
(5xx9r  state 5:  read a consecutive x.  done.

(4yy6r  
(6yy9r  state 6:  read a consecutive y.  done.

(5yy4r  not a consecutive pair.  Try for the next pair
(6xx4r

(4  8r  state 8:  there are no consecutive pairs.
(8cc8r  -- non final state.  This is never executed.