center in black ball-point pen, circled: 4; center verso in black ball-point pen, circled: 4; lower center verso in black ball-point pen: bruin en blaun
- M.C. Escher: A Centennial Tribute, National Gallery of Art, Washington; San Diego Museum of Art; The Chrysler Museum of Art, Norfolk, 1997-1999.
- "M.C. Escher", Knoxville Museum of Art, 2000.
- Bool, F.H. et al. M.C. Escher: His Life and Complete Graphic Work. Amsterdam: Meulenhoff, 1981; English-language edition, New York: Harry N. Abrams, 1982.