[2008.10.12]
This is the same as 2007.3.12 but can be compiled with g++-4.3

[2007.3.12]
Fixed the inefficiency bug in zverify_df. Thanks to Allen Van Gelder and 
Tjark Weber.

[2004.11.15 Simplified]
This is just a simplified version of 2004.5.13. Many portions of dead 
codes are removed. Some of codes are re-written and re-formatted for 
easy reading. You might experience a little speedup. Please switch back
to 2004.5.13 if the functionalities you need are removed in the simplified 
version.

[2004.5.13]
Some performace update. This is the version we used for SAT04 competition. 
Please consult our website for the detailed description.

[2003.12.04]
Fixed:
1. Various bugs in add_clause_incr(). We would like to thank Alexander 
   Smith from University of Toronto for his suggestion and experiments on 
   this issue.
2. SAT_HOOK added.
3. unset_force_terminate added.

[2003.11.04]
Fixed:
1. Compile under g++ 3.3 and above
2. Assertion error for certain instances in core extraction
3. A typo in run_till_fix. Now it takes the second argument as the max 
number of iterations to run as intended.

[2003.10.09]
Fixes in this release:
1. Bug fixed for time overflow after 2147 seconds.
2. The Perl script run_till_fix is updated such that it works for cnf 
files located in other directory.
3. zverify_df.cpp now also verifies the conflict clause given in 
resolve_trace with the one constructed by zverify itself using the 
information given in resolve_trace.
[2003.7.22]
NOTE: If your code is in C instead of C++, please use SAT_C.h instead of 
SAT.h as the header file. 

This is a new (as of June, 2003)  release of zchaff, a SAT solver from
Princeton University. The main difference between this one and the 
previous (2001.2.17) version are listed in the following:
1. This version of zchaff has incremental SAT solving capability
   In practice, many SAT instances are related in the sense that they only
   differ in a small number of clauses. Zchaff can solve a set of
   such instances incrementally, leveraging the knowledge (clauses) learned
   from previous runs to help current runs. This feature can only be invoked
   through the functional call interface. Please read SAT.h for more
   information about assigning clauses with Group IDs and how to delete
   clause or add clauses by groups.
                                                                                
                                    
2. This version of zchaff is certifiable
   Now zchaff can produce a verifiable trace that can be checked by a third
   party checker. To invoke this, modify zchaff_solver.cpp and uncomment
   #define VERIFY_ON and compile again. Now zchaff will produce a trace
   called resolution_trace after each run and this can be checked by
   zverify_bf or zverify_df, which are two checkers based on breadth-first 
   and depth-first search.
                                                                                
                                    
3. This version of zchaff can produce an unsatisfiable core from an 
   unsatisifable formula Unsatisfiable core extraction can be useful for 
   some applications. This version of zchaff implement the idea presented 
   in our SAT 2003 paper about extracting unsat cores.
                                                                                
4. This version can compile under gcc 3.x.
                                    
5. This version fixed a couple of serious bugs in the previous version. 
   (But may have introduced other bugs :().
                                                                                
                                    

How to use: 
  the main executable is zchaff. The command line is 
                zchaff CNF_FILE [TimeLimit]
  Other executables will print out a help info when executed with no 
  argument.

  run_till_fix can obtain a small core by iteratively run core extraction. 
  Do turn
  VERIFY_ON in zchaff_solver.cpp when compile. 

For any questions or bug reports, please send email to 
Yogesh Mahajan at yogism@Princeton.EDU

Thanks.

The SAT Group at Princeton University