Swart, E. R. The philosophical implications of the four-color problem. (English) Zbl 0464.05032 Am. Math. Mon. 87, 697-707 (1980). MSC: 05C15 00A30 PDFBibTeX XMLCite \textit{E. R. Swart}, Am. Math. Mon. 87, 697--707 (1980; Zbl 0464.05032) Full Text: DOI
Haken, Wolfgang Combinatorial aspects of some mathematical problems. (English) Zbl 0424.05030 Proc. int. Congr. Math., Helsinki 1978, Vol. 2, 953-961 (1980). MSC: 05C15 PDFBibTeX XML