spot/picosat/picosat.h

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#ifdef __cplusplus
extern "C" {
#endif

#ifndef picosat_h_INCLUDED
#define picosat_h_INCLUDED
/*------------------------------------------------------------------------*/

#include <stdlib.h>
#include <stdio.h>
#include <stddef.h>

/*------------------------------------------------------------------------*/
/* The following macros allows for users to distiguish between different
 * versions of the API.  The first 'PICOSAT_REENTRANT_API' is defined for
 * the new reentrant API which allows to generate multiple instances of
 * PicoSAT in one process.  The second 'PICOSAT_API_VERSION' defines the
 * (smallest) version of PicoSAT to which this API conforms.
 */
#define PICOSAT_REENTRANT_API
#define PICOSAT_API_VERSION 953		/* API version */

/*------------------------------------------------------------------------*/
/* These are the return values for 'picosat_sat' as for instance
 * standardized by the output format of the SAT competition.
 */
#define PICOSAT_UNKNOWN         0
#define PICOSAT_SATISFIABLE     10
#define PICOSAT_UNSATISFIABLE   20

/*------------------------------------------------------------------------*/
struct PicoSAT; //forward declaration
typedef struct PicoSAT PicoSAT;

/*------------------------------------------------------------------------*/

const char *picosat_version (void);
const char *picosat_config (void);
const char *picosat_copyright (void);

/*------------------------------------------------------------------------*/
/* You can make PicoSAT use an external memory manager instead of the one
 * provided by LIBC. But then you need to call these three function before
 * 'picosat_init'.  The memory manager functions here all have an additional
 * first argument which is a pointer to the memory manager, but otherwise
 * are supposed to work as their LIBC counter parts 'malloc', 'realloc' and
 * 'free'.  As exception the 'resize' and 'delete' function have as third
 * argument the number of bytes of the block given as second argument.
 */

typedef void * (*picosat_malloc)(void *, size_t);
typedef void * (*picosat_realloc)(void*, void *, size_t, size_t);
typedef void (*picosat_free)(void*, void*, size_t);

/*------------------------------------------------------------------------*/

PicoSAT * picosat_init (void);          /* constructor */

PicoSAT * picosat_minit (void * state,
			 picosat_malloc,
			 picosat_realloc,
			 picosat_free);

void picosat_reset (PicoSAT *);         /* destructor */

/*------------------------------------------------------------------------*/
/* The following five functions are essentially parameters to 'init', and
 * thus should be called right after 'picosat_init' before doing anything
 * else.  You should not call any of them after adding a literal.
 */

/* Set output file, default is 'stdout'.
 */
void picosat_set_output (PicoSAT *, FILE *);

/* Measure all time spent in all calls in the solver.  By default only the
 * time spent in 'picosat_sat' is measured.  Enabling this function might
 * for instance triple the time needed to add large CNFs, since every call
 * to 'picosat_add' will trigger a call to 'getrusage'.
 */
void picosat_measure_all_calls (PicoSAT *);

/* Set the prefix used for printing verbose messages and statistics.
 * Default is "c ".
 */
void picosat_set_prefix (PicoSAT *, const char *);

/* Set verbosity level.  A verbosity level of 1 and above prints more and
 * more detailed progress reports on the output file, set by
 * 'picosat_set_output'.  Verbose messages are prefixed with the string set
 * by 'picosat_set_prefix'.
 */
void picosat_set_verbosity (PicoSAT *, int new_verbosity_level);

/* Disable/Enable all pre-processing, currently only failed literal probing.
 *
 *  new_plain_value != 0    only 'plain' solving, so no preprocessing
 *  new_plain_value == 0    allow preprocessing
 */
void picosat_set_plain (PicoSAT *, int new_plain_value);

/* Set default initial phase:
 *
 *   0 = false
 *   1 = true
 *   2 = Jeroslow-Wang (default)
 *   3 = random initial phase
 *
 * After a variable has been assigned the first time, it will always
 * be assigned the previous value if it is picked as decision variable.
 * The initial assignment can be chosen with this function.
 */
void picosat_set_global_default_phase (PicoSAT *, int);

/* Set next/initial phase of a particular variable if picked as decision
 * variable.  Second argument 'phase' has the following meaning:
 *
 *   negative = next value if picked as decision variable is false
 *
 *   positive = next value if picked as decision variable is true
 *
 *   0        = use global default phase as next value and
 *              assume 'lit' was never assigned
 *
 * Again if 'lit' is assigned afterwards through a forced assignment,
 * then this forced assignment is the next phase if this variable is
 * used as decision variable.
 */
void picosat_set_default_phase_lit (PicoSAT *, int lit, int phase);

/* You can reset all phases by the following function.
 */
void picosat_reset_phases (PicoSAT *);

/* Scores can be erased as well.  Note, however, that even after erasing
 * scores and phases, learned clauses are kept.  In addition head tail
 * pointers for literals are not moved either.  So expect a difference
 * between calling the solver in incremental mode or with a fresh copy of
 * the CNF.
 */
void picosat_reset_scores (PicoSAT *);

/* Reset assignment if in SAT state and then remove the given percentage of
 * less active (large) learned clauses.  If you specify 100% all large
 * learned clauses are removed.
 */
void picosat_remove_learned (PicoSAT *, unsigned percentage);

/* Set some variables to be more important than others.  These variables are
 * always used as decisions before other variables are used.  Dually there
 * is a set of variables that is used last.  The default is
 * to mark all variables as being indifferent only.
 */
void picosat_set_more_important_lit (PicoSAT *, int lit);
void picosat_set_less_important_lit (PicoSAT *, int lit);

/* Allows to print to internal 'out' file from client.
 */
void picosat_message (PicoSAT *, int verbosity_level, const char * fmt, ...);

/* Set a seed for the random number generator.  The random number generator
 * is currently just used for generating random decisions.  In our
 * experiments having random decisions did not really help on industrial
 * examples, but was rather helpful to randomize the solver in order to
 * do proper benchmarking of different internal parameter sets.
 */
void picosat_set_seed (PicoSAT *, unsigned random_number_generator_seed);

/* If you ever want to extract cores or proof traces with the current
 * instance of PicoSAT initialized with 'picosat_init', then make sure to
 * call 'picosat_enable_trace_generation' right after 'picosat_init'.   This
 * is not necessary if you only use 'picosat_set_incremental_rup_file'.
 *
 * NOTE, trace generation code is not necessarily included, e.g. if you
 * configure PicoSAT with full optimzation as './configure.sh -O' or with

 * you do not get any results by trying to generate traces.
 *
 * The return value is non-zero if code for generating traces is included
 * and it is zero if traces can not be generated.
 */
int picosat_enable_trace_generation (PicoSAT *);

/* You can dump proof traces in RUP format incrementally even without
 * keeping the proof trace in memory.  The advantage is a reduction of
 * memory usage, but the dumped clauses do not necessarily belong to the
 * clausal core.  Beside the file the additional parameters denotes the
 * maximal number of variables and the number of original clauses.
 */
void picosat_set_incremental_rup_file (PicoSAT *, FILE * file, int m, int n);

/* Save original clauses for 'picosat_deref_partial'.  See comments to that
 * function further down.
 */
void picosat_save_original_clauses (PicoSAT *);

/* Add a call back which is checked regularly to notify the SAT solver
 * to terminate earlier.  This is useful for setting external time limits
 * or terminate early in say a portfolio style parallel SAT solver.
 */
void picosat_set_interrupt (PicoSAT *,
                            void * external_state,
			    int (*interrupted)(void * external_state));

/*------------------------------------------------------------------------*/
/* This function returns the next available unused variable index and
 * allocates a variable for it even though this variable does not occur as
 * assumption, nor in a clause or any other constraints.  In future calls to
 * 'picosat_sat', 'picosat_deref' and particularly for 'picosat_changed',
 * this variable is treated as if it had been used.
 */
int picosat_inc_max_var (PicoSAT *);

/*------------------------------------------------------------------------*/
/* Push and pop semantics for PicoSAT.   'picosat_push' opens up a new
 * context.  All clauses added in this context are attached to it and
 * discarded when the context is closed with 'picosat_pop'.  It is also
 * possible to nest contexts.
 *
 * The current implementation uses a new internal variable for each context.
 * However, the indices for these internal variables are shared with
 * ordinary external variables.  This means that after any call to
 * 'picosat_push', new variable indices should be obtained with
 * 'picosat_inc_max_var' and not just by incrementing the largest variable
 * index used so far.
 *
 * The return value is the index of the literal that assumes this context.
 * This literal can only be used for 'picosat_failed_context' otherwise
 * it will lead to an API usage error.
 */
int picosat_push (PicoSAT *);

/* This is as 'picosat_failed_assumption', but only for internal variables
 * generated by 'picosat_push'.
 */
int picosat_failed_context (PicoSAT *, int lit);

/* Returns the literal that assumes the current context or zero if the
 * outer context has been reached.
 */
int picosat_context (PicoSAT *);

/* Closes the current context and recycles the literal generated for
 * assuming this context.  The return value is the literal for the new
 * outer context or zero if the outer most context has been reached.
 */
int picosat_pop (PicoSAT *);

/* Force immmediate removal of all satisfied clauses and clauses that are
 * added or generated in closed contexts.  This function is called
 * internally if enough units are learned or after a certain number of
 * contexts have been closed.  This number is fixed at compile time
 * and defined as MAXCILS in 'picosat.c'.
 *
 * Note that learned clauses which only involve outer contexts are kept.
 */
void picosat_simplify (PicoSAT *);

/*------------------------------------------------------------------------*/
/* If you know a good estimate on how many variables you are going to use
 * then calling this function before adding literals will result in less
 * resizing of the variable table.  But this is just a minor optimization.
 * Beside exactly allocating enough variables it has the same effect as
 * calling 'picosat_inc_max_var'.
 */
void picosat_adjust (PicoSAT *, int max_idx);

/*------------------------------------------------------------------------*/
/* Statistics.
 */
int picosat_variables (PicoSAT *);                      /* p cnf <m> n */
int picosat_added_original_clauses (PicoSAT *);         /* p cnf m <n> */
size_t picosat_max_bytes_allocated (PicoSAT *);
double picosat_time_stamp (void);                       /* ... in process */
void picosat_stats (PicoSAT *);                         /* > output file */
unsigned long long picosat_propagations (PicoSAT *);	/* #propagations */
unsigned long long picosat_decisions (PicoSAT *);	/* #decisions */
unsigned long long picosat_visits (PicoSAT *);		/* #visits */

/* The time spent in calls to the library or in 'picosat_sat' respectively.
 * The former is returned if, right after initialization
 * 'picosat_measure_all_calls' is called.
 */
double picosat_seconds (PicoSAT *);

/*------------------------------------------------------------------------*/
/* Add a literal of the next clause.  A zero terminates the clause.  The
 * solver is incremental.  Adding a new literal will reset the previous
 * assignment.   The return value is the original clause index to which
 * this literal respectively the trailing zero belong starting at 0.
 */
int picosat_add (PicoSAT *, int lit);

/* As the previous function, but allows to add a full clause at once with an
 * at compiled time known size.  The list of argument literals has to be
 * terminated with a zero literal.  Literals beyond the first zero literal
 * are discarded.
 */
int picosat_add_arg (PicoSAT *, ...);

/* As the previous function but with an at compile time unknown size.
 */
int picosat_add_lits (PicoSAT *, int * lits);

/* Print the CNF to the given file in DIMACS format.
 */
void picosat_print (PicoSAT *, FILE *);

/* You can add arbitrary many assumptions before the next 'picosat_sat'
 * call.  This is similar to the using assumptions in MiniSAT, except that
 * for PicoSAT you do not have to collect all your assumptions in a vector
 * yourself.  In PicoSAT you can add one after the other, to be used in the
 * next call to 'picosat_sat'.
 *
 * These assumptions can be interpreted as adding unit clauses with those
 * assumptions as literals.  However these assumption clauses are only valid
 * for exactly the next call to 'picosat_sat', and will be removed
 * afterwards, e.g. in following future calls to 'picosat_sat' after the
 * next 'picosat_sat' call, unless they are assumed again trough
 * 'picosat_assume'.
 *
 * More precisely, assumptions actually remain valid even after the next
 * call to 'picosat_sat' has returned.  Valid means they remain 'assumed'
 * internally until a call to 'picosat_add', 'picosat_assume', or a second
 * 'picosat_sat', following the first 'picosat_sat'.  The reason for keeping
 * them valid is to allow 'picosat_failed_assumption' to return correct
 * values.
 *
 * Example:
 *
 *   picosat_assume (1);        // assume unit clause '1 0'
 *   picosat_assume (-2);       // additionally assume clause '-2 0'
 *   res = picosat_sat (1000);  // assumes 1 and -2 to hold
 *                              // 1000 decisions max.
 *
 *   if (res == PICOSAT_UNSATISFIABLE)
 *     {
 *       if (picosat_failed_assumption (1))
 *         // unit clause '1 0' was necessary to derive UNSAT
 *
 *       if (picosat_failed_assumption (-2))
 *         // unit clause '-2 0' was necessary to derive UNSAT
 *
 *       // at least one but also both could be necessary
 *
 *       picosat_assume (17);  // previous assumptions are removed
 *                             // now assume unit clause '17 0' for
 *                             // the next call to 'picosat_sat'
 *
 *       // adding a new clause, actually the first literal of
 *       // a clause would also make the assumptions used in the previous
 *       // call to 'picosat_sat' invalid.
 *
 *       // The first two assumptions above are not assumed anymore.  Only
 *       // the assumptions, since the last call to 'picosat_sat' returned
 *       // are assumed, e.g. the unit clause '17 0'.
 *
 *       res = picosat_sat (-1);
 *     }
 *   else if (res == PICOSAT_SATISFIABLE)
 *     {
 *       // now the assignment is valid and we can call 'picosat_deref'
 *
 *       assert (picosat_deref (1) == 1));
 *       assert (picosat_deref (-2) == 1));
 *
 *       val = picosat_deref (15);
 *
 *       // previous two assumptions are still valid
 *
 *       // would become invalid if 'picosat_add' or 'picosat_assume' is
 *       // called here, but we immediately call 'picosat_sat'.  Now when
 *       // entering 'picosat_sat' the solver knows that the previous call
 *       // returned SAT and it can safely reset the previous assumptions
 *
 *       res = picosat_sat (-1);
 *     }
 *   else
 *     {
 *       assert (res == PICOSAT_UNKNOWN);
 *
 *       // assumptions valid, but assignment invalid
 *       // except for top level assigned literals which
 *       // necessarily need to have this value if the formula is SAT
 *
 *       // as above the solver nows that the previous call returned UNKWOWN
 *       // and will before doing anything else reset assumptions
 *
 *       picosat_sat (-1);
 *     }
 */
void picosat_assume (PicoSAT *, int lit);

/*------------------------------------------------------------------------*/
/* This is an experimental feature for handling 'all different constraints'
 * (ADC).  Currently only one global ADC can be handled.  The bit-width of
 * all the bit-vectors entered in this ADC (stored in 'all different
 * objects' or ADOs) has to be identical.
 *
 * TODO: also handle top level assigned literals here.
 */
void picosat_add_ado_lit (PicoSAT *, int);

/*------------------------------------------------------------------------*/
/* Call the main SAT routine.  A negative decision limit sets no limit on
 * the number of decisions.  The return values are as above, e.g.
 * 'PICOSAT_UNSATISFIABLE', 'PICOSAT_SATISFIABLE', or 'PICOSAT_UNKNOWN'.
 */
int picosat_sat (PicoSAT *, int decision_limit);

/* As alternative to a decision limit you can use the number of propagations
 * as limit.  This is more linearly related to execution time. This has to
 * be called after 'picosat_init' and before 'picosat_sat'.
 */
void picosat_set_propagation_limit (PicoSAT *, unsigned long long limit);

/* Return last result of calling 'picosat_sat' or '0' if not called.
 */
int picosat_res (PicoSAT *);

/* After 'picosat_sat' was called and returned 'PICOSAT_SATISFIABLE', then
 * the satisfying assignment can be obtained by 'dereferencing' literals.
 * The value of the literal is return as '1' for 'true',  '-1' for 'false'
 * and '0' for an unknown value.
 */
int picosat_deref (PicoSAT *, int lit);

/* Same as before but just returns true resp. false if the literals is
 * forced to this assignment at the top level.  This function does not
 * require that 'picosat_sat' was called and also does not internally reset
 * incremental usage.
 */
int picosat_deref_toplevel (PicoSAT *, int lit);

/* After 'picosat_sat' was called and returned 'PICOSAT_SATISFIABLE' a
 * partial satisfying assignment can be obtained as well.  It satisfies all
 * original clauses.  The value of the literal is return as '1' for 'true',
 * '-1' for 'false' and '0' for an unknown value.  In order to make this
 * work all original clauses have to be saved internally, which has to be
 * enabled by 'picosat_save_original_clauses' right after initialization.
 */
int picosat_deref_partial (PicoSAT *, int lit);

/* Returns non zero if the CNF is unsatisfiable because an empty clause was
 * added or derived.
 */
int picosat_inconsistent  (PicoSAT *);

/* Returns non zero if the literal is a failed assumption, which is defined
 * as an assumption used to derive unsatisfiability.  This is as accurate as
 * generating core literals, but still of course is an overapproximation of
 * the set of assumptions really necessary.  The technique does not need
 * clausal core generation nor tracing to be enabled and thus can be much
 * more effective.  The function can only be called as long the current
 * assumptions are valid.  See 'picosat_assume' for more details.
 */
int picosat_failed_assumption (PicoSAT *, int lit);

/* Returns a zero terminated list of failed assumption in the last call to
 * 'picosat_sat'.  The pointer is valid until the next call to
 * 'picosat_sat' or 'picosat_failed_assumptions'.  It only makes sense if the
 * last call to 'picosat_sat' returned 'PICOSAT_UNSATISFIABLE'.
 */
const int * picosat_failed_assumptions (PicoSAT *);

/* Returns a zero terminated minimized list of failed assumption for the last
 * call to 'picosat_sat'.  The pointer is valid until the next call to this
 * function or 'picosat_sat' or 'picosat_mus_assumptions'.  It only makes sense
 * if the last call to 'picosat_sat' returned 'PICOSAT_UNSATISFIABLE'.
 *
 * The call back function is called for all successful simplification
 * attempts.  The first argument of the call back function is the state
 * given as first argument to 'picosat_mus_assumptions'.  The second
 * argument to the call back function is the new reduced list of failed
 * assumptions.
 *
 * This function will call 'picosat_assume' and 'picosat_sat' internally but
 * before returning reestablish a proper UNSAT state, e.g.
 * 'picosat_failed_assumption' will work afterwards as expected.
 *
 * The last argument if non zero fixes assumptions.  In particular, if an
 * assumption can not be removed it is permanently assigned true, otherwise
 * if it turns out to be redundant it is permanently assumed to be false.
 */
const int * picosat_mus_assumptions (PicoSAT *, void *,
                                     void(*)(void*,const int*),int);

/* Compute one maximal subset of satisfiable assumptions.  You need to set
 * the assumptions, call 'picosat_sat' and check for 'picosat_inconsistent',
 * before calling this function.  The result is a zero terminated array of
 * assumptions that consistently can be asserted at the same time.  Before
 * returing the library 'reassumes' all assumptions.
 *
 * It could be beneficial to set the default phase of assumptions
 * to true (positive).  This can speed up the computation.
 */
const int * picosat_maximal_satisfiable_subset_of_assumptions (PicoSAT *);

/* This function assumes that you have set up all assumptions with
 * 'picosat_assume'.  Then it calls 'picosat_sat' internally unless the
 * formula is already inconsistent without assumptions, i.e.  it contains
 * the empty clause.  After that it extracts a maximal satisfiable subset of
 * assumptions.
 *
 * The result is a zero terminated maximal subset of consistent assumptions
 * or a zero pointer if the formula contains the empty clause and thus no
 * more maximal consistent subsets of assumptions can be extracted.  In the
 * first case, before returning, a blocking clause is added, that rules out
 * the result for the next call.
 *
 * NOTE: adding the blocking clause changes the CNF.
 *
 * So the following idiom
 *
 * const int * mss;
 * picosat_assume (a1);
 * picosat_assume (a2);
 * picosat_assume (a3);
 * picosat_assume (a4);
 * while ((mss = picosat_next_maximal_satisfiable_subset_of_assumptions ()))
 *   process_mss (mss);
 *
 * can be used to iterate over all maximal consistent subsets of
 * the set of assumptions {a1,a2,a3,a4}.
 *
 * It could be beneficial to set the default phase of assumptions
 * to true (positive).  This might speed up the computation.
 */
const int *
picosat_next_maximal_satisfiable_subset_of_assumptions (PicoSAT *);

/* Similarly we can iterate over all minimal correcting assumption sets.
 * See the CAMUS literature [M. Liffiton, K. Sakallah JAR 2008].
 *
 * The result contains each assumed literal only once, even if it
 * was assumed multiple times (in contrast to the maximal consistent
 * subset functions above).
 *
 * It could be beneficial to set the default phase of assumptions
 * to true (positive).  This might speed up the computation.
 */
const int *
picosat_next_minimal_correcting_subset_of_assumptions (PicoSAT *);

/* Compute the union of all minmal correcting sets, which is called
 * the 'high level union of all minimal unsatisfiable subset sets'
 * or 'HUMUS' in our papers.
 *
 * It uses 'picosat_next_minimal_correcting_subset_of_assumptions' and
 * the same notes and advices apply.  In particular, this implies that
 * after calling the function once, the current CNF becomes inconsistent,
 * and PicoSAT has to be reset.  So even this function internally uses
 * PicoSAT incrementally, it can not be used incrementally itself at this
 * point.
 *
 * The 'callback' can be used for progress logging and is called after
 * each extracted minimal correcting set if non zero.  The 'nhumus'
 * parameter of 'callback' denotes the number of assumptions found to be
 * part of the HUMUS sofar.
 */
const int *
picosat_humus (PicoSAT *,
               void (*callback)(void * state, int nmcs, int nhumus),
	       void * state);

/*------------------------------------------------------------------------*/
/* Assume that a previous call to 'picosat_sat' in incremental usage,
 * returned 'SATISFIABLE'.  Then a couple of clauses and optionally new
 * variables were added (a new variable is a variable that has an index
 * larger then the maximum variable added so far).  The next call to
 * 'picosat_sat' also returns 'SATISFIABLE'. If this function
 * 'picosat_changed' returns '0', then the assignment to the old variables
 * is guaranteed to not have changed.  Otherwise it might have changed.
 *
 * The return value to this function is only valid until new clauses are
 * added through 'picosat_add', an assumption is made through
 * 'picosat_assume', or again 'picosat_sat' is called.  This is the same
 * assumption as for 'picosat_deref'.
 *
 * TODO currently this function might also return a non zero value even if
 * the old assignment did not change, because it only checks whether the
 * assignment of at least one old variable was flipped at least once during
 * the search.  In principle it should be possible to be exact in the other
 * direction as well by using a counter of variables that have an odd number
 * of flips.  But this is not implemented yet.
 */
int picosat_changed (PicoSAT *);

/*------------------------------------------------------------------------*/
/* The following six functions internally extract the variable and clausal
 * core and thus require trace generation to be enabled with
 * 'picosat_enable_trace_generation' right after calling 'picosat_init'.
 *
 * TODO: using these functions in incremental mode with failed assumptions
 * has only been tested for 'picosat_corelit' thoroughly.  The others
 * probably only work in non-incremental mode or without using
 * 'picosat_assume'.
 */

/* This function determines whether the i'th added original clause is in the
 * core.  The 'i' is the return value of 'picosat_add', which starts at zero
 * and is incremented by one after a original clause is added (that is after
 * 'picosat_add (0)').  For the index 'i' the following has to hold:
 *
 *   0 <= i < picosat_added_original_clauses ()
 */
int picosat_coreclause (PicoSAT *, int i);

/* This function gives access to the variable core, which is made up of the
 * variables that were resolved in deriving the empty clause.
 */
int picosat_corelit (PicoSAT *, int lit);

/* Write the clauses that were used in deriving the empty clause to a file
 * in DIMACS format.
 */
void picosat_write_clausal_core (PicoSAT *, FILE * core_file);

/* Write a proof trace in TraceCheck format to a file.
 */
void picosat_write_compact_trace (PicoSAT *, FILE * trace_file);
void picosat_write_extended_trace (PicoSAT *, FILE * trace_file);

/* Write a RUP trace to a file.  This trace file contains only the learned
 * core clauses while this is not necessarily the case for the RUP file
 * obtained with 'picosat_set_incremental_rup_file'.
 */
void picosat_write_rup_trace (PicoSAT *, FILE * trace_file);

/*------------------------------------------------------------------------*/
/* Keeping the proof trace around is not necessary if an over-approximation
 * of the core is enough.  A literal is 'used' if it was involved in a
 * resolution to derive a learned clause.  The core literals are necessarily
 * a subset of the 'used' literals.
 */

int picosat_usedlit (PicoSAT *, int lit);
/*------------------------------------------------------------------------*/
#endif

#ifdef __cplusplus
}
#endif