Litteratur. Box containing books and booklets about Skilling, Bi-coloured issues, Bogtryksudgaver. I.e Lasse Nielsen work The bicoloured stamps of Denmark vol. I-VI, catalougue “postvæsenets samling af danske frimærker”, 1932, 4 RBS plating by Hans Schønning and Erik Paaskesen all 3 volumes x 2 etc.