Consider for instance: $ aptitude why mailutils i muttprint Recommends mutt | sylpheed | gnus | xfmail | exmh | mail-reader i A mailutils Provides mail-reader Here, one can see that mailutils provides mail-reader. $ aptitude --show-summary=all-packages why mailutils Packages requiring mailutils: muttprint R: mail-reader P<- mail-reader But here one has mail-reader on both sides of "P<-". I suppose that this should have been muttprint R: mail-reader P<- mailutils