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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 get_ast_field_name(ast):
 """Return the normalized field name for the given AST node."""

    replacements = {
        # We always rewrite the following field names into their proper underlying counterparts.
        TYPENAME_META_FIELD_NAME: '@class'
    }
    base_field_name = ast.name.value
    normalized_name = replacements.get(base_field_name, base_field_name)
    return normalized_name