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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

1. cite journal |title="null" |journal=The Oxford English Dictionary, Draft Revision March 2004 |url=http://dictionary.oed.com |year=2004 |accessdate=2007-04-05
2. 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.

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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.