Give Type Definition For Scalar Type Called Circle

Give a type definition for a scalar type called CIRCLE, what selectors and The-operators apply to this type? Also:
a. Define a set of read only operators to compute the diameter, circumference, and area of a given circle.
b. Define an update operator to double the radius of a given circle (more precisely, to update a given Circle variable in such a way that its circle value is unchanged except that the radius is twice what it was before).

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