I'm trying to understand what a one-parameter group of transformations really is. At one lecture I was told that they are trivial lie groups. In Arnold's "Ordinary Differential Equations" they are defined as an action by the group of real numbers; a collection of transformations parametrised by the real parameter t (time), and as being the mathematical equivalent of a two-sided deterministic process. I can more or less understand all this, but still feel some confusion. For example, is there such a thing as a two-parameter group of transformations? n-parameter?