module main {
  // Shared and local variables
  var s : int;
  var y0 : boolean;
  var y1 : boolean;

  // Constants for the processes
  const p0 : int = 0;
  const p1 : int = 1;

  // Initial conditions
  init {
    s = 1;
    y0 = false;
    y1 = false;
  }

  // Transition rules for process P0
  next {
    case
      // Noncritical section
      !y0: {
        y0' = true;
        s' = p0;
      }
      // Critical section
      y0 && ((y1 == false) || (s != p0)): {
        y0' = false;
      }
      // Default case
      default: {
        y0' = y0;
        s' = s;
      }
    esac
  }

  // Transition rules for process P1
  next {
    case
      // Noncritical section
      !y1: {
        y1' = true;
        s' = p1;
      }
      // Critical section
      y1 && ((y0 == false) || (s != p1)): {
        y1' = false;
      }
      // Default case
      default: {
        y1' = y1;
        s' = s;
      }
    esac
  }

  // Property: Mutual Exclusion
  invariant mutual_exclusion : !(y0 && y1);

  // Property: Starvation Freedom
  invariant starvation_freedom : (y0 -> (y1 == false || s != p0)) && (y1 -> (y0 == false || s != p1));

  control {
    check;
    print_results;
  }
}
