There are two aspects that we defer to future work. First, the systems designed here assumed that the input are valid claim sentences. To make use of such systems, one needs to develop mechanisms to recognize valid argumentative structures. In addition, we ignore trustworthiness and credibility issues, important research issues that are addressed in other works. 
 Question: What challenges are highlighted?
one needs to develop mechanisms to recognize valid argumentative structures we ignore trustworthiness and credibility issues