升级到 20.04 时，我遇到了以下问题：
An unresolvable problem occurred while calculating the upgrade.
This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.
如果有的话，如何确定要删除哪个包？
我/var/log/dist-upgrade/apt.log
收到很多类似的行：
Broken libk3b7:amd64 Breaks on libk3b7-extracodecs:amd64 < 17.12.3-0ubuntu3 | 19.12.3-0ubuntu1 @ii umH > (< 18.08.3~)
Considering libk3b7-extracodecs:amd64 2 as a solution to libk3b7:amd64 4
Upgrading libk3b7-extracodecs:amd64 due to Breaks field in libk3b7:amd64
Investigating (9) libk3b7-extracodecs:amd64 < 17.12.3-0ubuntu3 -> 19.12.3-0ubuntu1 @ii umU Ib >
这是否表明存在问题？
输出sudo apt-update是干净的：
Hit:1 http://files.eid.belgium.be/debian bionic InRelease
Hit:2 http://archive.canonical.com/ubuntu bionic InRelease
Hit:3 http://archive.canonical.com bionic InRelease
Hit:4 http://us.archive.ubuntu.com/ubuntu bionic InRelease
Get:5 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
Hit:6 https://download.sublimetext.com apt/stable/ InRelease
Get:7 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]
Get:8 http://us.archive.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]
Hit:9 http://files2.eid.belgium.be/debian bionic InRelease
Hit:10 https://repo.skype.com/deb stable InRelease
Fetched 252 kB in 3s (76.6 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.
然后我禁用了除规范存储库之外的所有存储库。我不再收到有关第三方软件的错误。我收到的只是错误消息：An unresolvable problem occurred while calculating the upgrade.