1. A computer-implemented method for forming a representation of a digital system, the method comprising: building, by a processor, a decomposed BDD representative of the digital system by successively building BDDs for a Boolean function forming a Boolean function space of the system partitioning, by the processor, the Boolean function space of the decomposed BDD during a process of composition of the decomposed BDD; and outputting a composed BDD for a partition in the partitioned Boolean function space for verifying the digital system.