由於ubuntu/debian軟件庫中有時候不同的庫更新速度不一致，apt-get 出出現如下的錯誤提示
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
libssl-dev: Depends: libssl0.9.8 (= 0.9.8k-7ubuntu8) but 0.9.8k-7ubuntu8.5 is to be installed
這個時候應該請令一個工具出馬了："aptitude"
使用這個工具，當某個庫依賴的庫與當前版本不一致時，aptitude 會嘗試降級當前這個庫的版本，同時解決降級這個庫對其它軟件的依賴性的影響， 最終成功安裝apt-get 沒法安裝的軟件
如：#aptitude install vim-gnome