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doi.org
Rosenthal, Mark. “The Prototypical Triangle of Paul Klee.” The Art Bulletin, vol. 64, no. 2, [Taylor & Francis, Ltd., College Art Association], 1982, pp. 299–310, https://doi.org/10.2307/3050222. “The title Niesen makes explicit another identity of the triangle besides the Egyptian pyramid. "Niesen" is the name of a pyramidally shaped mountain in the Bernese Alps on Lake Thun, not far from Klee's childhood home near Bern. The area was a favorite of Klee's for hiking and vacationing; in 1915 he spent several days with his friend Louis Millet in the town of Gunten, which faces the Niesen from directly across the lake. Klee's study of the mountain from a dramatic vantage point recalls his affirmation, six years earlier, that Cézanne was "the teacher par excellence." As in Cézanne's Mont Ste.-Victoire paintings (Fig. 2), Klee, in Niesen, contrasts the strength of the mountain stretching to the skies with a patchy landscape below.”
