@ARTICLE {, title = {Matematické nástroje - Extremálny princíp}, author = {Vrábel, Peter}, journal = {Obzory matematiky, fyziky a informatiky}, year = {2009}, volume = {38}, number = {1}, pages = {31--34}, issn = {1335-4981}, abstract = {If a set of objects of some mathematical task can be suitable ordered, then it is natural to focus on the least or the greatest object. These special elements can be used as the instrument to solve the task. This mathematical method is illustrated on solutions of various tasks in the paper.}, }