code: @Override
  	public PExp defaultSBinaryExp(SBinaryExp node, Substitution question)
  			throws AnalysisException
  	{
  		PExp subl = node.getLeft().clone().apply(main, question);
  		PExp subr = node.getRight().clone().apply(main, question);
  		node.setLeft(subl.clone());
  		node.setRight(subr.clone());
  		return node;
  	}
docs: Let's try to do most stuff with S family