TODO: Explain ordinalization and ordinalizers here.
Arguments
Limitations
TODO: Be sure to note the highly restrictive assumptions made about
ordinalizer functions, especially as noted e.g. in connection with
the internal function G (defined in 'exact.R').
Validity
The validity of an ordinalizer might well be programmatically testable.
If so, all this discussion might well be carried out in documentation
for a validity-testing function.