What, you might ask, is a mobil duo? It is a movablepair of pawns standing side by side on either the two center squares e4 and d4 (or e5 and d5 as black) or c4 and d4, or e4 and f4. What’s so great about it? Well, number one, your opponent has four squares that he can’t use when you have a mobil duo. Every move he has to think about how he can’t place any of his good pieces on those four squares that are covered by e4 and d4. He is constrained. He is cramped. He has to work around those squares. He should challenge those pawns by c5, e5, or d5 if he can. Break up that mobil duo. What else is so great about it? It’s mobil. You can push it and thereby often push through your agenda on the board. Push his pieces around. It might not be the right time to push them right away. Just because they are mobil doesn’t mean you have to move them. In fact, because of the constraining effect they have you should refrain from moving them as long as possible.