def explain_aw(fsm, state, phi, psi):
    """
    Explain why state of fsm satisfies A phi W psi.
    
    fsm -- the fsm;
    state -- a state of fsm satisfying A phi W psi;
    phi -- the set of states of fsm satifying phi;
    psi -- the set of states of fsm satifying psi.
    """
    pass
