Neighborhood of a Vertex

Consider the following graph:

The set of all vertices in $G$ that are adjacent to a vertex $v$ is called the neighborhood of $v$ and denoted by $N(v)$.

$$ N_{\text{outgoing}}(A) = \{B, C\} $$

$$ N_{\text{incoming}}(C) = \{A, D\} $$

Exercise Name all the vertices adjacent to vertex $D$ in two groups – incoming neighbors and outgoing neighbors: