There are several situations in which it would be advantageous to allow route preferences to be dependent on which neighbor is to receive the route. This idea could be realised in many possible ways and could interact differently with other elements of route choice, such as filtering: not all of these will have the property that a unique routing solution can always be found. We develop an algebraic model of route selection to aid in the analysis of neighbor-specific preferences in multipath routing. Using this model, we are able to identify a set of such routing schemes in which convergence is guaranteed.