User:Jorge_Stolfi/DoW Wall Street Journal: Wikipedia loosing Volunteers

Lemma. For any two elements a and b (st. ab=ba), of order i and j, there is an element of order lcm(i,j). Proof: We can assume ${\displaystyle i\bot j}$, since otherwise we can replace a with an element of order ${\displaystyle i/{\text{lcd))(i,j)}$, namely ${\displaystyle a^((\text{lcd))(i,j)))$. Consider ord(ab)=k. k divides ij. a^k=(b^{-1})^k where b^{-1} has also order j. ord(a^k) divides i = ord(b^k) = divides j, so a^k=b^k=1. So i divides k and j divides k.

• Degeneracy (graph theory) (e.g. O(d)-time adjacency structure).
• De_Bruijn_graph, Line graph
• non-trivial "densest subgraph" algorithms, see non-dynamic refs in Near-Optimal Fully Dynamic Densest Subgraph
• Wikipedia_talk:WikiProject_Mathematics/Typography
• max-width
• PageRank

• fokonolona (maybe also Balinese 'seka')

• Modern approaches to early Islamic history – The New Cambridge History of Islam

Arabic

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