cs = {'Alice', 'Charlie', 'Denise'}
bio = {'Denise', 'Eva', 'Fred'}
chem = {'Bob', 'Fred', 'Alice'}

def remove_list_duplicates(some_list):
    '''returns a new list that has duplicates removed'''
    return list(set(some_list))

def find_duplicates(some_list):
    '''return a set of numbers that appear
    at least twice in some_list'''
    
    dups_set = set()    # just the duplicates
    elem_set = set()    # all the elements in the list
    
    for entry in some_list:
        len_before = len(elem_set)
        elem_set.add(entry)
        len_after = len(elem_set)
        if len_before == len_after:
            # entry is a duplicate
            dups_set.add(entry)
    return dups_set
        
# should return {3, 8}
find_duplicates([3, 4, 3, 5, 8, 0, 8, 8])