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The basic template is a pentagon, having two pairs of 
equal sides. In one pair the sides are at 60 to one another, 
in the other at 120. 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 rotational 
relations.
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