Example: A ring.

• We cannot implement:

  • addition
  • negation
  • multiplication
  • inversion
  • "zero"
  • "one"
  • check if zero

• We can implement:

  • subtraction (because of addition and negation)
  • exponantiation a
  • embedding of Z, Q.
  • check for equality
  • polynomials over this ring
  • etc.

n

The good news is:

Object Oriented programming allows having objects which do not implement everything!(Concept of overriding abstract methods)

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