packages kept back

[David Abrahams]

How do I fix this problem?

  $ sudo apt-get upgrade
  Password:
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  The following packages have been kept back:
    dpkg-dev fakeroot g++ g++-4.1 libc6-dev libstdc++6-4.1-dev
  0 upgraded, 0 newly installed, 0 to remove and 6 not upgraded.

I can get details about the unmet dependencies, but that doesn't help
me understand how to fix them.  For example:

The following packages have unmet dependencies:
  g++-4.1: Depends: gcc-4.1-base (= 4.1.2-15ubuntu2) but 4.1.2-0ubuntu4 is to be installed
           Depends: gcc-4.1 (= 4.1.2-15ubuntu2) but 4.1.2-0ubuntu4 is to be installed
           Depends: libstdc++6-4.1-dev (= 4.1.2-15ubuntu2) but it is not going to be installed
           Depends: libc6 (>= 2.6-1) but 2.5-0ubuntu14 is to be installed

I don't know why the older versions of packages such as libc6 are "to
be installed," nor what to do about it.

TIA,

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com