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File docs/Nurikabe_Strategies.txt

 limits of its number), an island can only expand into one cell, then that
 cell will be white.
 
-#. If an Island reaches certain points that reaching them consumes all of its
+#. If an Island reaches certain points which consume all of its
 number, then its white edge points can be marked with black in the opposite
 direction to its extent.
 
 We can see that the island should expand into the leftmost gray/unknown cell 
 or else it will need to take a costly detour which will consume the rest of its
 number.
+
+#. Islands that can expand in several different manners must mark all the 
+common black cells inflected by these ways in this way. For example:
+
++------
+|[2][G]
+|[G][G]
+
+The lower-right [G] cell must be black because it will be black whether the
+2 expands to the right or to the bottom.
+
+In addition, if we have:
+
+    x1 x2 x3 x4 
+y1     [B][B][B]
+y2  [B][4][W][B]
+y3  [B][G][W][B]
+y4     [G][G][B]
+
+The the 4-cell region can only expand into (x2,y3) or (x3,y4) so 
+[G](x2,y4) must be black.
+