We demonstrate a family of propositional formulas in conjunctive normal form so that a formula of size $N$ requires size $2^{Omega(sqrt[7]{N/logN})}$ to refute using the tree-like OBDD refutation system of Atserias, Kolaitis and Vardi with respect to all variable orderings. All known symbolic quantifier elimination algorithms for satisfiability generate tree-like proofs when run on unsatisfiable CNFs, so this lower bound applies to the run-times of these algorithms. Furthermore, the lower bound generalizes earlier results on OBDD-based proofs of unsatisfiability in that it applies for all variable orderings, it applies when the clauses are processed according to an arbitrary schedule, and it applies when variables are eliminated via quantification.

This version differs from the earlier version in that some of the proofs have been cleaned up and made shorter.

We demonstrate a family of propositional formulas in conjunctive normal form
so that a formula of size $N$ requires size $2^{\Omega(\sqrt[7]{N/logN})}$
to refute using the tree-like OBDD refutation system of
Atserias, Kolaitis and Vardi
with respect to all variable orderings.
All known symbolic quantifier elimination algorithms for satisfiability
generate tree-like proofs when run on unsatisfiable CNFs, so this lower bound
applies to the run-times of these algorithms.
Furthermore, the lower bound generalizes earlier
results on OBDD-based
proofs of unsatisfiability in that it applies for all variable
orderings, it applies when the clauses are processed according to
an arbitrary schedule, and it applies when variables are eliminated via
quantification.

Brief summary of differences between TR07-007 and TR07-009 Comment on: TR07-009

A brief summary the differences between the main results in TR07-007 and TR07-009