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The basic template is a pentagon, having both a pair of equal and 
parallel sides, and another pair of equal, adjacent sides making equal 
and opposite angles with a direction taken here to be horizontal. The 
five vertices can be fixed anywhere within these constraints, and the 
mid-point of the remaining side is then also fixed. The associated 
distortions allowed within each pair of related segments are indicated 
by the arrowheads, as are their translational, rotational and glide
reflective relations.  
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