Identity Map
The map which assigns every member of a set A to the same element id_A. It is identical to the identity function.
See also
Donkin's Theorem, Identity Function, Zero MapExplore with Wolfram|Alpha
WolframAlpha
More things to try:
Cite this as:
Weisstein, Eric W. "Identity Map." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/IdentityMap.html