In combinative Optimization, one speaks about together discrete to indicate " units; fondamentalement" discrete, it is in general of the finished units or units which have primarily same nature as the whole of the natural whole . In any rigor, a unit is discrete only compared to a topological Espace. I.e., that a subset F of a topological space will be known as discrete so for all X of F it exists a Voisinage container X and no other element of F . The discrete units all are countable but notice that the whole of the rational is countable but not discrete. The typical example of a whole of real discrete infinite and limited is that of the 1/n for all whole N not no one.