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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 as_txt(self):
 """Text rendering of error response. Designed for use with Image API version 1.1 and above where the error response is suggested to be text or html but not otherwise specified. Intended to provide useful information for debugging. """

        s = "IIIF Image Server Error\n\n"
        s += self.text if (self.text) else 'UNKNOWN_ERROR'
        s += "\n\n"
        if (self.parameter):
            s += "parameter=%s\n" % self.parameter
        if (self.code):
            s += "code=%d\n\n" % self.code
        for header in sorted(self.headers):
            s += "header %s=%s\n" % (header, self.headers[header])
        return s