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Opera Opera (trình duyệt web) Opera tại Việt Nam Opera Nova Bydgoszcz Opera Software Opera GX (trình duyệt web) Opera Mini Operação Prato Opera Leśna Operatsiya Silent StormTài liệu tham khảo
WikiPedia: Opera http://www.opera-opera.com.au/archives.htm http://www.opera-opera.com.au/plotind.htm http://www.american.com/archive/2007/july-august-m... http://www.britannica.com/EBchecked/topic/348741/L... http://www.britannica.com/EBchecked/topic/429776/o... http://books.google.com/books?id=fovWU9Prkj0C&lpg=... http://www.historicopera.com http://operabase.com http://www.stageagent.com/browse/showtype/opera http://opera.stanford.edu/main.html