See section 11.9.4 for parallelograms in the plane.
The parallelogram command takes three points as arguments.
The parallelogram command returns and draws a parallelogram.
If the arguments are A, B and C, then the
parallelogram has the form ABCD.
Input:
then:
Output:
The parallelogram command takes an optional fourth argument,
which is a variable the fourth vertex is assigned to.
Input:
then:
Output: