Write down a bijection to show that the following two graphs are

isomorphic.

A company has $21$ employees, $11$ of which are junior employees and $10$

of which are senior employees. Each junior employee is asked to

connect with exactly $5$ other employees. Each senior employee is asked

to connect with exactly $6$ other employees.

$($Assume contacts are undirected, i$.$e$.$ Employee A connecting with

Employee B implies that Employee B connects with Employee A$.)$

Regard each employee as a node on a graph. Considering the degree of

each node, show that no such arrangement of connections exists.