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The basic template is a hexagon, having one pair of equal and 
opposite sides which are parallel. The two sides at one end of these 
are equal in length, and make equal and opposite angles with the line 
joining the ends of the parallel sides, taken here to be horizontal. The 
six vertices are fixed within these constraints, and the mid-points of 
the other two sides are then fixed. The associated distortions allowed 
within each related pair of segments are indicated by the arrowheads, 
as are their tanslational, rotational, and glide reflective relations.
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