Perhaps you should try some spelling variations:
petria » petris (Expand Search), petra (Expand Search), petruia (Expand Search), petroia (Expand Search), peria (Expand Search)
petri » petrui (Expand Search), petroi (Expand Search), peri (Expand Search)
petr » petru (Expand Search), petro (Expand Search), per (Expand Search)
petriov » petruiov (Expand Search), petroiov (Expand Search), periov (Expand Search), petrov (Expand Search)
petroou » petruoou (Expand Search), petrooou (Expand Search), peroou (Expand Search)
petroi » petruoi (Expand Search), petrooi (Expand Search), peroi (Expand Search), petro (Expand Search), petrov (Expand Search), petrow (Expand Search)
petrouoi » petruouoi (Expand Search), petroouoi (Expand Search), perouoi (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 ((((petri OR petria) OR petr) OR petriov) OR ((petroou OR (petroi OR petrouoi)) OR peter)) o.s.~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "fop ((((petri OR petria) OR petr) OR petriov) OR ((petroou OR (petroi OR petrouoi)) OR peter)) o.s.".
• Adding a wildcard symbol may retrieve word variants: fop ((((petri OR petria) OR petr) OR petriov) OR ((petroou OR (petroi OR petrouoi)) OR peter)) o.s.*.