#include <stdio.h>
#include <gmp.h>
#define GODFREY 0
#if GODFREY
  #define CHECK_BIT(var,pos) (((var) & (pos)) ? 2LL : -2LL)
#else
  #define CHECK_BIT(var,pos) (((var) & (pos)) ? 1LL : 0LL)
#endif
#define n 4
#define NPOS (2*n)

mpz_t bigsum;
mpz_t tmp;
long long int prod[n];
unsigned int k;

inline void updatesum(unsigned int odd)
{
    mpz_set_si(tmp,1);
    for(k=0; k < n; k++)
    {
      if(prod[k] == 0LL) 
      {
	return;
      }
      mpz_mul_si(tmp,tmp,prod[k]);
    }
    if(odd) mpz_sub(bigsum,bigsum,tmp);
    else mpz_add(bigsum,bigsum,tmp);
}

int main(int argc, char *argv[])
{
  unsigned int delta[n] = {2,3,5,6};
  unsigned long long int i,swp,min;
  unsigned long long int gray = 0;
  unsigned long long int bigN = (1LL<<(NPOS));
  mpz_init(bigsum);
  mpz_init(tmp);
  for (k=0; k < n; k++) prod[k] = 0LL;
  for(i=0LL; i < bigN; i++)
  {
    min = i & (-i); // bit changed in graycode
    gray ^= min; // graycode

    if(min&gray) // +1
    {

      swp=min>>delta[0];
      for (k=0; k < n && swp; k++, swp=min>>delta[k])
      {
	prod[k] += CHECK_BIT(gray,swp);
      }

      swp=min<<delta[0];
      for (k=0; k < n && swp < bigN; k++, swp=min<<delta[k])
      {
	prod[k] += CHECK_BIT(gray,swp);
      }
    }
    else // 0
    {
      swp=min>>delta[0];
      for (k=0; k < n && swp; k++, swp=min>>delta[k])
      {
	prod[k] -= CHECK_BIT(gray,swp);
      }

      swp=min<<delta[0];
      for (k=0; k < n && swp < bigN; k++, swp=min<<delta[k])
      {
	prod[k] -= CHECK_BIT(gray,swp);
      }
    }
    updatesum(i&1);
  }
  #if GODFREY
    gmp_printf("bigSum %Zd\n", bigsum);
    mpz_fdiv_q_2exp(bigsum, bigsum, NPOS);
  #endif
  gmp_printf("%Zd skolem sequenses over {", bigsum);
  for (k=0; k < n; k++)
    printf("%d,", delta[k]);
  printf("}\n");
}