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Eva Engel; Heidi Ulrich; Rudolf Vasold; Burkhard König; Michael Landthaler; Rudolf Süttinger; Wolfgang Bäumler (2008). "Azo Pigments and a Basal Cell Carcinoma at the Thumb". Dermatology. 216 (1): 76–80. doi:10.1159/000109363. PMID18032904. S2CID34959909.
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