class Cell {
  var x: int;
  var y: Cell;
  
  method a1()
    requires acc(x,y); // ERROR: amount is not integer
  {
  }
  
  method a2()
    requires acc(x,n); // ERROR: unknown variable
  {
  }
  
  method a3()
    requires acc(x,rd(rd(1))); // ERROR: invalid permission expression
  {
  }
  
  method a4()
    requires acc(x,rd*(y)); // ERROR: invalid permission expression
  {
  }
  
  method a5()
    requires acc(x,rd(this.mu)); // ERROR: invalid type inside rd
    requires acc(x,rd(null)); // ERROR: invalid type inside rd
    requires acc(x,rd(true)); // ERROR: invalid type inside rd
  {
  }
  
  method a6()
    requires acc(x,rd(x)*rd(x)); // ERROR: permission multiplication not allowed
  {
  }
  
}