/* Quadratic equation solver */
/* Last edited on 2007-01-04 00:23:27 by stolfi */

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

typedef struct Eqn {
  int n;       /* Number of variables. */
  long int *c; /* Coefficient matrix, packed: {c[i,j] = c[i+j*(j+1)/2]}. */
  long int *m; /* Variable {x[i]} has range {[0..m[i]]} for {i>0}, {[1..1]} for {i=0}. */
} Eqn;

typedef struct Sol {
  int n;        /* Number of variables. */
  long int x;   /* Variable values. */
} Sol;

Sol *solve(Eqn *eq);
/* Tries to find a solution {so} to the equation {eq}, where 
  {so.x[0] = 1} and each {so.x[i]}, for {i > 0}, ranges in {[0..eq.b[i]}.
  The equation is {SUM{eq.c[i,j]*x[i]*x[j] : 0 \leq i \leq j < n}}. 
  Returns NULL if {eq} has no solution. */

Sol *solve(Eqn *eq)
{
  Sol *so;
  
  if ((so = trivial_solution(eq)) != NULL)
    { return so; }
  else 
    { solve(reduce(...
  /* Reduce the equation modulo 2. */
  
  /* Express solutions in terms of new binary variables. */
  ...
  
}

bool_t solve_mod_2(Eqn *eq, Sol *so)
/* Finds a 0-1 solution to the question {eq}, interpreted modulo 2. */
{
  /* Enqueue all equations as having uncertain status. */
  while (/* queue is not empty */)
    { /* remove an equation from the queue. */
      /* Check all 
  
}

void main(int argc, char **argv)
{