Example - from class Magnitude

The relational operators, used for comparisons, are defined in class Magnitude. If you look at these carefully you will notice an interesting circularity. Less than or equal is defined in terms of less than, and of equal. Greater than or equal in terms of less than or equal. Less than in terms of less than or equal and not equal. And so on. This would seem to necessarily imply an infinite circularity.

[audio] [real] Text to accompany slide12, in Chapter 14 of An Introduction to Object-Oriented Programming