Maximum Degree of Vertex in Simple Graph

Theorem
Let $G = \struct {V, E}$ be a simple graph.

Let $\card V$ denote the order of $G$.

Then no vertex of $G$ has a degree higher than $\card V - 1$.

Proof
By definition, a simple graph has no loops or multiple edges.

So a vertex can be incident to only as many edges that will join it to all the other vertices once each.

There are $\card V - 1$ other vertices.

Hence the result.