1. Circuits and Trees in Oriented Linear Graphs;van Aardenne-Ehrenfest;Simon Stevin,1951
2. A Combinatorial Problem;de Bruijn;Nederl. Akad. Wetensch. Proc. A,1946
3. Some Properties of Line Digraphs;Harary;Rend. Circ. Mat. Palermo,1960
4. The Dissection of Equilateral Triangles into Equilateral Triangles;Tutte,1948