The dual-coding theory enunciates that these two systems can operate independently, as well as interdependently. Nurses provide care both interdependently, for example, with physicians, and independently as nursing professionals. Hubbard later sought to unify societies that were working interdependently to promote emigration. Controlling each wheel interdependently, AYC and ASC worked together to improve both safety and performance. In most areas, the police were able to hold out interdependently. This structure forces students to be self-directed, independent and to work interdependently. Improvisation can take place as a solo performance, or interdependently in ensemble with other players. Value and price are therefore determined interdependently, though they remain distinct. It works interdependently with the other hospitals in the trust to provide a complete service. The structural parts of society (e.g. families, work) function interdependently to help society function.