function decreaseApproval(address _spender,uint256 _subtractedValue) public returns (bool) {


     if(_spender == leaseExchange) {
       require(allowed[msg.sender][_spender].sub(_subtractedValue) >= LEMB.getAmountForUserMining(msg.sender));
     }
     super.decreaseApproval(_spender,_subtractedValue);
   }