#### Answer

The given relation is a function.
Domain: $\left\{4, 5, 6\right\}$
Range: $\left\{1\right\}$

#### Work Step by Step

RECALL:
(i) A function is a relation where every first coordinate is paired with exactly one second coordinate.
(ii) The domain of a relation is a set that contains all the first coordinates.
(iii) The range of a relation is a set that contains all the second coordinates.
Note that each first coordinate of the relation is paired with only one second coordinate. Thus, the given relation is a function.
The domain of the relation is $\left\{4, 5, 6\right\}$.
The range of the relation is $\left\{1\right\}$.