Checking whether an element ist NOT part of a list.

Hello,

it may sound funny, but I would like to check whether an element is not
part of list.
But there exist no list:notIn in CWM.
Does anybody has an idea how to check whether an element is not part of
a list?
This feature is needed in a rule as the following.

{ ?p a kmdl:Person.
   ?k a kmdl:KDescriptor.
   ?p kmdl:executes [a kmdl:Function; kmdl:demands ?k].
   ?k list:notIn ?p.kmdl:knowlegde. 
} => { ?p kmdl:missing ?k }.

Thank you,
    Nane