Okay, but while "abc" is not a number, it is also the string "abc". NaN is special in that all it tells you is that the value is not a number -- it doesn't tell you what it is. In order to return a true value from an equality test, it isn't enough to know that both values are not a number, you have to know what they actually are.
If it is not known what is in the p variable, then the variable is indeterminate; it has exactly the same status as a variable that has not been initialized. In this case, the behavior upon accessing the variable should be undefined.
I agree with making accesses of NaN-valued variables undefined behavior, so that not comparing equal is then a possible consequence of undefined behavior.
I don't agree with defining the unequal comparison as the required behavior. To define the behavior is tantamount to the recognition that a NaN is something: an object. A variable can have a defined value which is that something, and that value must obey the Law of Identity.
