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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 getHeadContent(self, req):
 """ Retrieve a list of header content from all installed themes on the site store. """

        site = ixmantissa.ISiteURLGenerator(self.store)
        for t in getInstalledThemes(self.store):
            yield t.head(req, site)