$**$

$*$ An Inventory implemented using a HashMap$<$Video,Record$>.$

$*$ Keys are Videos; Values are Records.

$*$

$*$ @objecttype Mutable Collection of Records

$*$ @objectinvariant

$*$ Every key and value in the map is non$-$null.

$*$ @objectinvariant

$*$ Each value r is stored under key r$.$video.

$*/$