Anotace:

"The geometry of triangles, polygons and circles in the Euclidean plane consists of many well known and forgotten theorems, and some mathematicians say that this type of geometry is old-fashioned. In the present talk I will show that still there are many interesting tasks and problems of this type, even in the Euclidean plane, but mainly also in non-Euclidean planes and/or in higher dimensions. This might stimulate even further research on simplices, polytopes and ball configurations in the Euclidean or non-Euclidean sense."