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The basic template is an isosceles triangle, having an 
angle of 120 between its two equal sides. Only its size 
can be altered and the three vertices are then fixed within 
this constraint. The mid-point of the odd side is then also 
fixed. The related distortions allowed to each of the two 
segments of this side and to the other two sides are 
indicated by the arrowheads, as are their rotational 
relations.

  
