Difference

Consider the following two events #A# and #B#:
\[\begin{array}{rcl}
A &=& \{8,\,9,\,12,\,13,\,15,\,16\}\\
B &=&\{4,\,8,\,9,\,10,\,15,\,20\}
\end{array}\]

What is the difference of #A# and #B#?

Note: Enter the elements in order from smallest to largest.

#A \,\backslash\, B = \{#, , #\}#