On approximation by circle plus-OBDDs

We show that for every V-OBDD of quasipolynomial size there is a circle plus-OBDD of quasipolynornial size computing the same function up to a small fraction of the inputs. We also prove that the final step in the approximation cannot be improved and discuss possibilities of proving non-approximability results and connections to lower bounds on matrix rigidity. (c) 2006 Elsevier B.V. All rights reserved.