  function burnFrom(address _from, uint256 _value) public returns (bool success) {
    balanceOf[_from] = balanceOf[_from].sub(_value);                           
    allowance[_from][msg.sender] = allowance[_from][msg.sender].sub(_value);    
    totalSupply = totalSupply.sub(_value);                               
    emit Burn(_from, _value);
    return true;
  }