समर्थ पद are those have a relationship or indicate ability with respect to another. Only the first pronounced of the समर्थ पद has the suffix applied. For example, उपगोः अपत्यं has अण् through तस्य अपत्यं. Out of the समर्थ two the प्रथम is उपगोः. Therefore, we have उपगु अण् - औपगव् अ - औपगवः.