For example, using "function" in the sense of multivalued functions, just as the square root function could be defined from , the function is defined so that . For a given real number , with , there are multiple (in fact, countably infinite) numbers such that ; for example, , but also , , etc. When only one value is desired, the function may be restricted to its principal branch. With this restriction, for each in the domain, the expression will evaluate only to a single value, called its principal value. These properties apply to all the inverse trigonometric functions.