Points de vue sur les valeurs aux entiers des formes quadratiques binaires
Résumé
The primary focus of this largely expository paper is to present different points of view on the values assumed by binary quadratic forms, sometimes with irrational coefficients, at integer values. Three different points of view are taken. One is the traditional approximation of real numbers by continued fractions, a second brings in the actions of the group ${\rm SL}_2(\Bbb{Z})$, and the third involves topological considerations of quotient spaces.