  --> tracing.TwoDShape(double, double)
  <-- tracing.TwoDShape(double, double)
  --> tracing.Circle(double, double, double)
  <-- tracing.Circle(double, double, double)
  --> tracing.TwoDShape(double, double)
  <-- tracing.TwoDShape(double, double)
  --> tracing.Circle(double, double, double)
  <-- tracing.Circle(double, double, double)
  --> tracing.Circle(double)
  <-- tracing.Circle(double)
  --> tracing.TwoDShape(double, double)
  <-- tracing.TwoDShape(double, double)
  --> tracing.Square(double, double, double)
  <-- tracing.Square(double, double, double)
  --> tracing.Square(double, double)
  <-- tracing.Square(double, double)
  --> double tracing.Circle.perimeter()
  <-- double tracing.Circle.perimeter()
c1.perimeter() = 12.566370614359172
  --> double tracing.Circle.area()
  <-- double tracing.Circle.area()
c1.area() = 12.566370614359172
  --> double tracing.Square.perimeter()
  <-- double tracing.Square.perimeter()
s1.perimeter() = 4.0
  --> double tracing.Square.area()
  <-- double tracing.Square.area()
s1.area() = 1.0
  --> double tracing.TwoDShape.distance(TwoDShape)
    --> double tracing.TwoDShape.getX()
    <-- double tracing.TwoDShape.getX()
    --> double tracing.TwoDShape.getY()
    <-- double tracing.TwoDShape.getY()
  <-- double tracing.TwoDShape.distance(TwoDShape)
c2.distance(c1) = 4.242640687119285
  --> double tracing.TwoDShape.distance(TwoDShape)
    --> double tracing.TwoDShape.getX()
    <-- double tracing.TwoDShape.getX()
    --> double tracing.TwoDShape.getY()
    <-- double tracing.TwoDShape.getY()
  <-- double tracing.TwoDShape.distance(TwoDShape)
s1.distance(c1) = 2.23606797749979
  --> String tracing.Square.toString()
    --> String tracing.TwoDShape.toString()
    <-- String tracing.TwoDShape.toString()
  <-- String tracing.Square.toString()
s1.toString(): Square side = 1.0 @ (1.0, 2.0) 
