Difference between revisions of "Surjection"
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| − | A surjection is a function | + | A '''surjection''' is a [[function]] which takes each value in its [[codomain]] at some value in its [[domain]]. That is, the [[range]] (or [[image]]) of the function is equal to its codomain. (For every function, the range is a subset of the codomain.) In adjectival form, we say that a function is ''surjective'' or ''onto''. |
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| + | For instance, the function <math>f: \mathbb Z \to \mathbb Z</math> defined by <math>f(x) = x+1</math> is surjective because every [[integer]] is one more than some other integer, but the function <math>f: \mathbb N \to\mathbb N</math> defined by <math>f(x) = x+1</math> is not surjective because there exists a [[natural number]] which is not one more than any other natural number. | ||
See also: | See also: | ||
| − | * [[bijection]] | + | * [[bijection|Bijection]] |
| − | * [[injection]] | + | * [[injection|Injection]] |
Revision as of 00:04, 27 June 2006
A surjection is a function which takes each value in its codomain at some value in its domain. That is, the range (or image) of the function is equal to its codomain. (For every function, the range is a subset of the codomain.) In adjectival form, we say that a function is surjective or onto.
For instance, the function 
defined by 
is surjective because every integer is one more than some other integer, but the function 
defined by is not surjective because there exists a natural number which is not one more than any other natural number.
See also:
