contention for /usr/lib64 in libc6 and base-files

[Larry Doolittle <ldoolitt@recycle.lbl.gov>]

If I try to install (update) libc6, I get

dpkg: error processing /var/cache/apt/archives/libc6_2.3.2.ds1-19.0.0.1.pure64_amd64.deb (--unpack):
 trying to overwrite `/usr/lib64', which is also in package base-files

If I try to install (update) base-files, I get

The following packages have unmet dependencies:
  base-files: PreDepends: libc6 (>= 2.3.2.ds1-19.0.0.1.pure64) but 2.3.2.ds1-19 is to be installed
  libc6-dev: Depends: libc6 (= 2.3.2.ds1-19.0.0.1.pure64) but 2.3.2.ds1-19 is to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).

And of course, apt-get -f install tries to install libc6, so
I'm back to square one.  How do I recover from this?

I understand from reading e.g.,
  http://lists.debian.org/debian-amd64/2004/12/msg00318.html
that some of these links are critical for the system's operation,
so I don't want to charge ahead without some idea where I'm going.

   - Larry