f):
        &#34;&#34;&#34;Returns Vset vfunc keys&#34;&#34;&#34;
        if isinstance(self.vfuncs, dict):
            return self.vfuncs.keys()
        return {}.keys()

    def __len__(self):
        return len(self.vfuncs)

    def __str__(self):
        return &#34;Vset(&#34; + self.name + &#34;)&#34;

    def __create_subkey(self, value):
        &#34;&#34;&#34;Helper function to construct `Subkey` with
        this Vset determining origin and output_matching
        &#34;&#34;&#34;
        return Sub