FOM: Conservative extensions

[Joseph Shoenfield]

     Steve's proof that ZF plus real choice is conservative over ZF for
second order arithmetic seems to be marred by a confusion between two
models of ZF.   The first, the class of sets constructible from a
real, does not necessarily satisfy choice; in fact, a popular axiom
is that this model satisfies AD.   The second, the class of sets
constructible from R (the set of reals) does not necessarily contain
all the reals.