Reference
Göran Nilson, Claes Andrén, Zbigniew Szyndlar (1994/1995): The systematic position of the Common Adder, Vipera berus (L.) (Reptilia, Viperidae), in North Korea and adjacent regions – Bonn zoological Bulletin - früher Bonner Zoologische Beiträge. – 45: 49 - 56.