How to construct a parallelogram with code (Smalltalk sketch)?
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How do I construct a parallelogram  with code (Smalltalk sketch )?
In particular how do I mark that opposite sides must have the same length?
An example of a parallelogram sketch is provided with the DrGeo release.
a parallelogram is a simple (non-self-intersecting) quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure. The congruence of opposite sides and opposite angles is a direct consequence of the Euclidean parallel postulate and neither condition can be proven without appealing to the Euclidean parallel postulate or one of its equivalent formulations.
 https://www.gnu.org/software/dr-geo/doc/en/Smalltalk-sketch.html#Smalltalk-sketch Dr.Geo Smalltalk sketches – (DSS) – are sketches entirely defined in the Smalltalk language.
When a sketch is defined with it, we can use all the power of the language to build a sketch, or to position some objects randomly to get a slightly different sketch at each execution of its Smalltalk code. Therefore, a Smalltalk sketch is freed from the constraints of the graphic user interface while reinforced by the Smalltalk language.