===== Partial function =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $X,Y$ |
| @#FFBB00: definiendum | @#FFBB00: $ f\in\text{PartialFunction}(X,Y) $ |
| @#55CCEE: context     | @#55CCEE: $ f \in \text{Rel}(X,Y) $ |
| @#55EE55: postulate   | @#55EE55: $ \langle x,a\rangle\in f \land \langle x,b\rangle\in f \Rightarrow a=b $ |

==== Discussion ====
The definition can be written as

$\{\langle x,a\rangle,\langle x,b\rangle\}\subseteq f \Rightarrow a=b.$

It says that each argument $x$ for the function can result in only one value. (functionality)
=== Reference ===
Wikipedia: 
[[http://en.wikipedia.org/wiki/Partial_function|Partial function]]
==== Parents ====
=== Subset of ===
[[Binary relation]]