Perhaps you should try some spelling variations:
petris » petri (Expand Search), petriis (Expand Search), petruis (Expand Search), petrois (Expand Search)
petra » petri (Expand Search), petru (Expand Search), petro (Expand Search), petria (Expand Search), petrua (Expand Search), petroa (Expand Search)
petriov » petrov (Expand Search), petriiov (Expand Search), petruiov (Expand Search), petroiov (Expand Search)
petroi » petri (Expand Search), petro (Expand Search), petrov (Expand Search), petrioi (Expand Search), petruoi (Expand Search), petrooi (Expand Search)
petr » petri (Expand Search), petru (Expand Search), petro (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 (petra OR petriov)) OR ((per OR petroi) OR (petr OR peter))) o.s.~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "fop ((petris OR (petra OR petriov)) OR ((per OR petroi) OR (petr OR peter))) o.s.".
• Adding a wildcard symbol may retrieve word variants: fop ((petris OR (petra OR petriov)) OR ((per OR petroi) OR (petr OR peter))) o.s.*.