Question #$8$: overloaded$\_$add$($d$,$ key, value$)$

$5$ pts

Given a dictionary $d,$ a key, and a value, this function adds the key:value pair to the dictionary $d.$ If the key doesn't already exist in the dictionary, this function should simply add it$.$ However, if the key already exists, then rather than overriding the previous value, the dictionary should start keeping a list of values for that key, in the order they are added.

Preconditions and Postconditions