Encyclopedia > Non-empty

  Article Content

Non-empty

A set is called non-empty (or nonempty) if it contains at least one element, and is therefore not the empty set.

The requirement that a set be non-empty is frequently found in mathematical hypotheses. One reason is that we can easily make logical errors when we make hypotheses about the empty set, which is often nonintuitive and can be tricky to reason about correctly (see Empty set for further discussion of this). Thus, this hypothesis of nonemptiness can often be removed under a more careful treatment. On the other hand, there certainly are times when the empty set is a special case and really does need to be excluded from a hypothesis.

A common example where both of these situations obtains is the axiom of choice. Although this axiom can be stated in several ways, for each standard way of stating it, there are two places where the term "nonempty" could be used. Often you will find the term used in both places, whereas in fact it is needed in only one. (See Axiom of choice for further discussion of this example).



All Wikipedia text is available under the terms of the GNU Free Documentation License

 
  Search Encyclopedia

Search over one million articles, find something about almost anything!
 
 
  
  Featured Article
Lake Ronkonkoma, New York

... 5,011 families residing in the town. The population density is 1,549.2/km² (4,010.1/mi²). There are 6,949 housing units at an average density of 546.4/km² ...

 
 
 
This page was created in 37.9 ms