def Lexicon(**rules):
for (lhs, rhs) in list(rules.items()):<EOL><INDENT>rules[lhs] = [word.strip() for word in rhs.split('<STR_LIT:|>')]<EOL><DEDENT>return rules<EOL>
Create a dictionary mapping symbols to alternative words.
    >>> Lexicon(Art = "the | a | an")
    {'Art': ['the', 'a', 'an']}