Perhaps you should try some spelling variations:
petris » petri (Expand Search), peteris (Expand Search), petriis (Expand Search), petruis (Expand Search)
petruv » petru (Expand Search), petrov (Expand Search), peteruv (Expand Search), petriuv (Expand Search), petruuv (Expand Search)
petrui » petri (Expand Search), petru (Expand Search), peterui (Expand Search), petriui (Expand Search), petruui (Expand Search)
petr » peter (Expand Search), petri (Expand Search), petru (Expand Search)
petruov » peteruov (Expand Search), petriuov (Expand Search), petruuov (Expand Search), petrov (Expand Search)

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: fop (((petris OR petruv) OR petrui) OR (petr OR (petruov OR petrui))) o.s.~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "fop (((petris OR petruv) OR petrui) OR (petr OR (petruov OR petrui))) o.s.".
• Adding a wildcard symbol may retrieve word variants: fop (((petris OR petruv) OR petrui) OR (petr OR (petruov OR petrui))) o.s.*.