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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 handle_molecular_activity_default(_: str, __: int, tokens: ParseResults) -> ParseResults: """Handle a BEL 2.0 style molecular activity with BEL default names."""

    upgraded = language.activity_labels[tokens[0]]
    tokens[NAMESPACE] = BEL_DEFAULT_NAMESPACE
    tokens[NAME] = upgraded
    return tokens