Petja poiskal knigu, no ne nasel eë, poetomu ne perestal iskat'.
Peter PF-look.for-pst.sg.masc.book, but not PF-find-pst.sg.masc.her, therefore not PF-stop-pst.sg.masc.look.for-INF
Peter looked for the book but didn't find it, therefore he didn't stop searching