How to remove entry in associative array?

Now that I know how to start with an empty associative array and fill it: what about the other way around and remove an entry form an associative array?

i.e. how to remove the element with key b in the code below:

:global rot13 ({});
:set ($rot13->"a") "n"
:set ($rot13->"b") "o"
:set ($rot13->"c") "p"

–jeroen

Calling :set on variable or array elements without any value seems to work like unset (v6.42.3), check this:

:global a {b=1}
/environment print
:set ($a->"b")
/environment print
:set $a
/environment print