Probably what is meant is the ones caught when you #'eql them iterating the first list, and not the lists within. So the result for your example would be just the first a removed of the second argument. (Assuming the first list is the ones that have to be deleted and the second the list to delete from)
You can write it using #'delete-if, with predicate being whether it is in list of things you want to delete. Or you can use #'loop/#'iter
and collect those you do not want deleted.