VAR
  
  a[4]
  b[4]
  c[4]

ASSIGN

  init(a) := 0;

  next(a) := sub(b, c);

  init(b) := 
    case
      oracle_b : 13;
      1 : 11;
    esac;
  
  next(b) := b;

  init(c) :=
    case
      oracle_c : 11;
      1 : 7;
    esac;
  
  next(c) := c;

-- SPEC AG a != 2
-- SPEC AG a != 4
-- SPEC AG a != 6
-- SPEC AG a != 0
SPEC AG(a = 0 | a = 2 | a = 4 | a = 6 | a = 0)
