code: def select(self, node):
          
          child = self.translate(node.child)
          return '[.${op}_{{{conditions}}}$ {child} ]'\
              .format(op=latex_operator[node.operator],
                      conditions=node.conditions, child=child)
docs: Translate a select node into a latex qtree node.
          :param node: a treebrd node
          :return: a qtree subtree rooted at the node