...
In this compliant solution, the CaseInsensitiveString.equals() method is simplified to only operation operate on instances of the CaseInsensitiveString class.
...
In the noncompliant code example, p1 and p2 compare equal and p2 and p3 compare equal but p1 and p3 compare unequal; violating the transitivity requirement. The problem is that the Card class has no knowledge of the XCard class and consequently cannot determine that p2 and p3 have different values for the field type. Unfortunately, it is impossible to extend an instantiable class (as opposed to an abstract class) by adding a value or field in the subclass while preserving the equals() contract.
...