From 1814 to 1819 he, or rather his admirers, were engaged in a long and angry controversy with Jens Immanuel Baggesen, who represented the old didactic school. This contest seems to have disturbed the peace of Oehlenschlägers mind and to have undermined his genius. His talent may be said to have culminated in the glorious cycle of verse-romances called Helge, published in 1814. The tragedy of Hagbarth og Signe, (1815), showed a distinct falling-off in style. In 1817 he went back to Paris, and published Hroars Saga and the tragedy of Fostbrødrene. In 1818 he was again in Copenhagen, and wrote the idyll of Den lille Hyrdedreng and the Eddaic cycle called Nordens Guder. His next productions were the Tragedy of Erik og Abel (1820) and Væringerne i Miklagaard (1826), and the epic of Hrolf Krake (1829). His last volumes were Tordenskjold (1833), Dronning Margrethe (1833), Sokrates (1835), Olaf den Hellige (1836), Knud den Store (1838), Dina (1842), Erik Glipping (1843), and Kiartan og Gudrun (1847). On his seventieth birthday, 14 November 1849, a public festival was arranged in his honour, and he was decorated by the king of Denmark under circumstances of great pomp. He died on 20 January 1850 and was buried in the cemetery of Frederiksberg. Immediately after his death his Recollections were published in two volumes.
Question: Which publications were two years apart from another publication?
Answer: Hagbarth og Signe | Hroars Saga | the tragedy of Fostbrødrene | Tordenskjold | Dronning Margrethe | Sokrates | Olaf den Hellige | Knud den Store