Several applications that manipulate both BDDs and ZDDs benefit from keeping a fixed correspondence between the order of the BDD variables and the order of the ZDD variables. If each BDD variable corresponds to a group of ZDD variables, then it is often desirable that the groups of ZDD variables be in the same order as the corresponding BDD variables. In the current implementation, CUDD allows the ZDD order to track the BDD order (but not vice versa). To have the ZDD order track the BDD order, the application calls Cudd_zddRealignEnable . The effect of this call can be reversed by calling Cudd_zddRealignDisable . When ZDD realignment is in effect, automatic reordering of ZDDs should be disabled.