A complete feedback planning algorithm must compute a feedback solution if one exists; otherwise, it must report failure. Section 8.4.1 parallels Section 8.2 by defining feedback plans and navigation functions for the case of a continuous state space. Section 8.4.2 indicates how to define a feasible feedback plan from a cell complex that was computed using cell decomposition techniques. Section 8.4.3 presents a combinatorial approach to computing an optimal navigation function and corresponding feedback plan in . Sections 8.4.2 and 8.4.3 allow the feedback plan to be a discontinuous vector field. In many applications, especially those in which dynamics dominate, some conditions need to be enforced on the navigation functions and their resulting vector fields. Section 8.4.4 therefore considers constraints on the allowable vector fields and navigation functions. This coverage includes navigation functions in the sense of Rimon-Koditschek , from which the term navigation function was introduced.