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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 is_common(schema):
 """ Is `schema` an common schema. Args: schema: Scheme to test. Returns: bool: ``True`` if schema is a common schema, otherwise ``False``. """

    if isinstance(schema, StreamSchema):
        return schema.schema() in _SCHEMA_COMMON
    if isinstance(schema, CommonSchema):
        return True
    if isinstance(schema, basestring):
        return is_common(StreamSchema(schema))
    return False