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Summary: Abstract
We introduce a new approach to Boolean satisfiability
(SAT) that combines backtrack search techniques and
zero-suppressed binary decision diagrams (ZBDDs). This
approach implicitly represents SAT instances using
ZBDDs, and performs search using an efficient implemen-
tation of unit propagation on the ZBDD structure. The
adaptation of backtrack search algorithms to such an
implicit representation allows for a potential exponential
increase in the size of problems that can be handled.
Introduction. Many efficient enhancements to the Davis-
Logemann-Loveland (DLL) backtrack-search procedure
have been proposed. These enhancements extended the ap-
plication of SAT solvers to large problem instances. Nev-
ertheless, despite these advances, the tremendous growth in
today's designs is outpacing the capabilities of existing
SAT solvers as these tend to explicitly represent the clause
database and lead to time and memory explosion.
Rather than explicitly representing the clause database
using arrays or linked lists, an alternative is to implicitly
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