def Rules(**rules):
    """Create a dictionary mapping symbols to alternative sequences.
    >>> Rules(A = "B C | D E")
    {'A': [['B', 'C'], ['D', 'E']]}
    """
    for (lhs, rhs) in rules.items():
        rules[lhs] = [alt.strip().split() for alt in rhs.split('|')]
    return rules
Create a dictionary mapping symbols to alternative sequences.
    >>> Rules(A = "B C | D E")
    {'A': [['B', 'C'], ['D', 'E']]}