Ian McIntosh wrote, partially agreeing with Nate Hayes' claim that
there is "NO way" to discuss level 2 without reference to level 3:
It also shows that you NEED to know some of the Level 3 details to
determine parts of the Level 2 abstract data type (eg, that Infinities
cannot have payloads - IF 754 had used different exponent field values
for NaNs versus Infinities, then Infinities could have had payloads).
Not so. I have no difficulty at all understanding Level 2 on its own
terms, including determining the cardinality of its support set.