The de Bruijn-Erd\"os-Hanani theorem
Abstract
The paper is devoted to a somewhat idiosyncratic account of the theorem of de Bruijn-Erd\"os and Hanani from the combinatorics of finite geometries and its various proofs. Among the proofs discussed are the original proofs by de Bruijn--Erd\"os and Hanani and few others. It is explained how one of the proofs was discovered, and how another one could have been discovered.
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