Ah.. but here PG is wondering into the opposite direction of what eekee is, if I understand correctly.. PG seems to be favoring the following distinction:
is .. checks if a is the same thing as b (like pointers referring to the same address in memory).
iso .. checks if the content at whatever a is pointing at is the same as whatever b is pointing at.
which is now violated by strings. I am not sure how numbers fit into this. In general I would favor the more commonly used 'has the same content as' to be is, and 'refers to the same entity' to be iso for brevity reasons.
But isn't iso short for isomorphic which, as I understand it, is the same as "these two things are equivalent" - which maps much more closely to "has the same content as," not "refers to the same entity"?