# This function from lecture may be useful as a model for some of
# your work on Problem Set 3.
#
# However, note that this function operates on lists, and you will
# need to modify it so that it operates on strings.

def rem_first(elem, values):
    """ removes the first occurrence of elem from the list values
    """
    if values == []:
        return []
    elif values[0] == elem:
        return values[1:]
    else:
        result_rest = rem_first(elem, values[1:])
        return [values[0]] + result_rest