I don't know if my Ubuntu system is on high or anything, but I realized that if you remove a package, you also lose your ability to install it again.

For example, when I remove a package called `dmd`, and search it, it just shows the package `dmd` without any description, with the tag `residual-config`. And if I try to install it, it will split an error back to me, says that the package `dmd` doesn't have any release candidate. And if I `purge` it, it will magically vanish when I search it, and install it will just say `No apt package "dmd"`.