GYO algorithm: Difference between revisions

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* Find an ear ''e'' in ''H''.
* Remove ''e'' and remove all vertices of ''H'' that are only in ''e''.
If the algorithm successfully eliminates all vertices, then the hypergraph is α-acylic. Otherwise, if the algorithm gets to a non-emtpyempty hypergraph that has no ears, then the original hypergraph was not α-acyclic:
 
{{Proof|proof=Assume first the GYO algorithm ends on the empty hypergraph, let <math>e_1,\ldots,e_m</math> be the sequence of ears that it has found, and let <math>H_0,\ldots,H_m</math> the sequence of hypergraphs obtained (in particular <math>H_0 = H</math> and <math>H_m</math> is the empty hypergraph). It is clear that <math>H_m</math>, the empty hypergraph, is <math>\alpha</math>-acyclic. One can then check that, if <math>H_n</math> is <math>\alpha</math>-acyclic then <math>H_{n-1}</math> is also <math>\alpha</math>-acyclic. This implies that <math>H_0</math> is indeed <math>\alpha</math>-acyclic.