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In Mathematics, the word

**null**(from German

*null*and Norwegian

*null*, which is from Latin

*nullus*, both meaning "zero", or "none")(1) may or may not have a meaning different from zero. Sometimes the symbol

**?**is used to distinguish "null" from

**0**.

In a Vector Space the null vector is the zero vector; in Set Theory, the null set is the set with zero elements; and in Measure Theory, a null set is a set with zero measure.

A mathematical mapping is said to be

*null potent*(or

*nilpotent*) if repeated application can map the whole domain into the null element.

A Null Space of a mapping is the part of the domain that is mapped into the null element of the image (the inverse image of the null element).

The

**null graph**or the

**empty graph**is the graph with no points and no lines. (2)

In statistics, a Null Hypothesis is a proposition presumed true unless statistical evidence indicates otherwise.

**Null**may refer to:

- /dev/null, the null device in Unix-like operating systems
- KK Null, a Japanese musician
- Null, in Law,
*having no legal validity* - Null (computer), a special value in computer programming
- Null (physics), a concept in
*electromagnetism*and*theoretical physics* - Null (SQL), a special value in SQL
- Null Allele (genetics), also see amorph
- Null Character, an ASCII value of 00 commonly used as a terminator, separator or filler
- Null Cipher, a
*ciphertext*symbol - Null Hypothesis, a hypothesis in statistics
- Null Morpheme (linguistics)
- Null Result, the absence of the expected result in a scientific experiment
- Nulls, worm-like remains of defeated characters in the animated program ReBoot

## References

- cite journal |title="null" |journal=The Oxford English Dictionary, Draft Revision March 2004 |url=http://dictionary.oed.com |year=2004 |accessdate=2007-04-05
- Harary, F. and Read, R., "Is the Null Graph a Pointless Concept?",
*Graphs and Combinatorics Conference*, George Washington University, Springer-Verlag, New York, NY, 1973.

*(can't find: GetWiki:disambig)*

*Some content adapted from the Pseudopedia article "Null" under the GNU Free Documentation License.*

*Some content adapted from the Pseudopedia article "Null_(mathematics)" under the GNU Free Documentation License.*

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