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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def keyword(tokens, expected):
 """Case-insensitive keyword match."""

    try:
        token = next(iter(tokens))
    except StopIteration:
        return

    if token and token.name == "symbol" and token.value.lower() == expected:
        return TokenMatch(None, token.value, (token,))