#. If marking a cell as white will make it reachable only by one island,
and as a result they will form a parly-diagonal loop of white cells, which
will segment the black master region, then the cell must be black.
+#. If we have something like:
+The if [G](x1,y2) is white, then (x2,y1) and (x2,y2) will be black which
+will form a 2*2 region of black cells which is impossible.