Typically, to limit the space of latent structures, certain assumptions have to be made to h. In our work, we assume that h must be from a space consisting of <cite>relaxed hybrid tree</cite> structures <cite>(Lu, 2014)</cite> . The <cite>relaxed hybrid trees</cite> are analogous to the hybrid trees, which was earlier introduced as a generative framework. One major distinction between these two types of representations is that the <cite>relaxed hybrid tree</cite> representations are able to capture unbounded long-distance dependencies in a principled way.