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Lenstra-Hurwitz Cliques In Real Quadratic Fields, Daniel S. Lopez

Master's Theses

Let $K$ be a number field and let $\OO_K$ denote its ring of integers. We can define a graph whose vertices are the elements of $\OO_K$ such that an edge exists between two algebraic integers if their difference is in the units $\OO_K^{\times}$. Lenstra showed that the existence of a sufficiently large clique (complete subgraph) will imply that the ring $\OO_K$ is Euclidean with respect to the field norm. A recent generalization of this work tells us that if we draw more edges in the graph, then a sufficiently large clique will imply the weaker (but still very interesting) conclusion …