1. Ahlswede, R., Cai, N.: Shadows and isoperimetry under the sequence-subsequence relation. Combinatorica 17(1), 11–29 (1997)
2. Ahlswede, R., Lebedev, V.: Shadows under the word-subword relation. In: Twelfth International Workshop on Algebraic and Combinatorial Coding Theory, Akademgorodok, Novosibirsk, pp. 16–19 (2010)
3. Ahlswede, R., Lebedev, V.: Shadows under the word-subword relation. Problems of Information Transmission 48(1), 30–45 (2012)
4. Chowdhury, A., Patkos, B.: Shadows and intersections in vector spaces. J. Combin. Theory Ser. A 117(8), 1095–1106 (2010)
5. Kruskal, J.B.: The Number of Simplices in a Complex, Mathematical Optimization Techniques, Berkeley, Los Angeles, pp. 251–278 (1963)