In set theory
, a projection
is one of two closely related types of functions
or operations, namely:
- A set-theoretic operation typified by the jth projection map, written , that takes an element of the cartesian product to the value .
- A function that sends an element x to its equivalence class under a specified equivalence relation E. The result of the mapping is written as [x] when E is understood, or written as [x]E when it is necessary to make E explicit.