/* X lt Y */

int fd_lt_filter(fd_constraint this)

{
  fd_int x, y;

  x = VAR(this, 0);
  y = VAR(this, 1);

#ifndef DISABLE_ENTAILED
  if (_fd_var_max(x) < _fd_var_min(y))

    fd__constraint_set_entailed(this);
#endif

  if (_fd_var_del_le(_fd_var_min(x), y))
    {

      if (fd_domain_empty(y))
	return FD_NOSOLUTION;

      _fd_revise_connected(NULL, y);
    }

  if (_fd_var_del_ge(_fd_var_max(y), x))

    {

      if (fd_domain_empty(x))
	return FD_NOSOLUTION;

      _fd_revise_connected(NULL, x);
    }

  return FD_OK;

}

int fd_lt_propagate2(fd_constraint this, fd_int culprit)

{
  fd_int revise;
  int changed = 0;

#if !defined(DISABLE_ENTAILED) && CONSTRAINT_TEMPS > 2

  if (_fd_var_max(VAR(this, 0)) < _fd_var_min(VAR(this, 1)))
    {
      fd__constraint_set_entailed(this);

      return FD_OK;

    }
#endif

  if (culprit == VAR(this, 0))
    {

      revise = VAR(this, 1);

      changed = _fd_var_del_le(_fd_var_min(culprit), revise);
    }
  else
    {
      revise = VAR(this, 0);

      changed = _fd_var_del_ge(_fd_var_max(culprit), revise);
    }

  if (changed && fd_domain_empty(revise))
    return FD_NOSOLUTION;

  if (changed)

    _fd_revise_connected(0, revise);

  return FD_OK;

}

int fd_lt_propagate(fd_constraint this, fd_int revise)
{

  int changed = 0;

  if (revise == VAR(this, 0))

    changed = _fd_var_del_ge(_fd_var_max(VAR(this, 1)), revise);

  else

    changed = _fd_var_del_le(_fd_var_min(VAR(this, 0)), revise);

  if (changed && fd_domain_empty(revise))
    return FD_NOSOLUTION;

#ifdef USE_ENTAILED

  if (_fd_var_max(VAR(this, 0)) < _fd_var_min(VAR(this, 1)))
    _fd_constraint_set_entailed(this);
#endif

  // XXX: enqueue further updates here?
  if (changed)
    _fd_revise_connected(this, revise);

  return FD_OK;
}

fd_constraint fd_lt(fd_int x, fd_int y)

{
  fd_constraint c = _fd_constraint_new(2, 0);

  if (c)

    {

      c->variables[0] = FD_INT2C_VAR(x); c->variables[1] = FD_INT2C_VAR(y);
#ifdef CONSTRAINT_CLASS
      c->kind = FD_CONSTR_LT;
#else /* CONSTRAINT_CLASS */
      c->propagator2 = fd_lt_propagate2;
      c->propagator = fd_lt_propagate;
#endif /* CONSTRAINT_CLASS */

      _fd_var_add_constraint(x, c);
      _fd_var_add_constraint(y, c);

      _fd_add_constraint(c);
    }

  return c;
}