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Markus Heinz. (1993). A Research Paper on the Copper-Plates of the Maps of J. B. Homann's First World Atlas (1707) and a Method for Identifying Different Copper-Plates of Identical-Looking Maps. Imago Mundi, 45(), 45–58. doi:10.2307/1151161 
An interview with Sci-Hub Founder Alexandra Elbakyan,Who exactly should pay for academic research