HoDoKu W-Wing
The cells {2} and {3}
<-> {0} and {1}
form a W-Wing pattern on the values
{4} and {5}.
In {6} there are only two cells ({2} and {3}) which may be
{5}, so one of those two cells must contain the value
{5}, and those two cells also have two siblings ({0}
and {1}) which can only be {4} or {5},
therefore one of those two siblings must contain the value
{4}, therefore any cells that are siblings of both the
siblings {0} and {1} may not be {4}.
Other occurrences of the value {4}
can therefore be removed from siblings of both {0} and {1},
ie {7}.