Legal drinking age. The legal drinking age is the age at which a person can legally consume or purchase alcoholic beverages. These laws cover a wide range of issues and behaviors, addressing when and where alcohol can be consumed.
An open system is a system that has external interactions. Such interactions can take the form of information, energy, or material transfers into or out of the system boundary, depending on the discipline which defines the concept.
As an open set is a set that is a neighborhood of all its points, a function : â is continuous at every point of X if and only if it is a continuous function. If X and Y are metric spaces, it is equivalent to consider the neighborhood system of open balls centered at x and f(x) instead of all neighborhoods.