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pragma solidity ^0.4.17;

// ----------------------------------------------------------------------------
// Burnable NVCT token contract
//
// Symbol           : NVCT
// Name             : nVision Cash Token
// Initial Supply   : 850,000,000
// Decimals         : 18

// ----------------------------------------------------------------------------
// Safe math
// ----------------------------------------------------------------------------
library SafeMath {
    function add(uint a, uint b) internal pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function sub(uint a, uint b) internal pure returns (uint c) {
        require(b <= a);
        c = a - b;
    }
    function mul(uint a, uint b) internal pure returns (uint c) {
        c = a * b;
        require(a == 0 || c / a == b);
    }
    function div(uint a, uint b) internal pure returns (uint c) {
        require(b > 0);
        c = a / b;
    }
}


// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
// ----------------------------------------------------------------------------
contract ERC20Interface {
    function totalSupply() public constant returns (uint);
    function balanceOf(address tokenOwner) public constant returns (uint balance);
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

contract Owned {
    address public owner;

    event OwnershipTransferred(address indexed _from, address indexed _to);

    function Owned() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address _newOwner) public onlyOwner {
        require(_newOwner != address(0x0));
        emit OwnershipTransferred(owner,_newOwner);
        owner = _newOwner;
    }
    
}

// ----------------------------------------------------------------------------
// ERC20 Token, with the addition of symbol, name and decimals and an
// initial fixed supply
// ----------------------------------------------------------------------------
contract NVCTToken is ERC20Interface, Owned {
    using SafeMath for uint;

    string public symbol;
    string public  name;
    uint8 public decimals;
    uint public _totalSupply;

    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowed;
    
    event Burn(address indexed burner, uint256 value);
    
    // ------------------------------------------------------------------------
    // Constructor
    // ------------------------------------------------------------------------
    function NVCTToken() public {
        symbol = "NVCT";
        name = "nVision Cash token";
        decimals = 18;
        _totalSupply = 850000000 * 10**uint(decimals);
        balances[owner] = _totalSupply;
        emit Transfer(address(0), owner, _totalSupply);
    }
    
    function() public payable {
        revert();
    }
    
    // ------------------------------------------------------------------------
    // Total supply
    // ------------------------------------------------------------------------
    function totalSupply() public constant returns (uint) {
        return _totalSupply;
    }


    // ------------------------------------------------------------------------
    // Get the token balance for account `tokenOwner`
    // ------------------------------------------------------------------------
    function balanceOf(address tokenOwner) public constant returns (uint balance) {
        return balances[tokenOwner];
    }


    // ------------------------------------------------------------------------
    // Transfer the balance from token owner's account to `to` account
    // - Owner's account must have sufficient balance to transfer
    // - 0 value transfers are allowed
    // ------------------------------------------------------------------------
    function transfer(address to, uint tokens) public returns (bool success) {
        if(balances[msg.sender] >= tokens && tokens > 0 && to!=address(0)) {
            balances[msg.sender] = balances[msg.sender].sub(tokens);
            balances[to] = balances[to].add(tokens);
            emit Transfer(msg.sender, to, tokens);
            return true;
        } else { return false; }
    }


    // ------------------------------------------------------------------------
    // Token owner can approve for `spender` to transferFrom(...) `tokens`
    // from the token owner's account
    //
    // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
    // recommends that there are no checks for the approval double-spend attack
    // as this should be implemented in user interfaces 
    // ------------------------------------------------------------------------
    function approve(address spender, uint tokens) public returns (bool success) {
        if(tokens > 0 && spender != address(0)) {
            allowed[msg.sender][spender] = tokens;
            emit Approval(msg.sender, spender, tokens);
            return true;
        } else { return false; }
    }


    // ------------------------------------------------------------------------
    // Transfer `tokens` from the `from` account to the `to` account
    // 
    // The calling account must already have sufficient tokens approve(...)-d
    // for spending from the `from` account and
    // - From account must have sufficient balance to transfer
    // - Spender must have sufficient allowance to transfer
    // - 0 value transfers are allowed
    // ------------------------------------------------------------------------
    function transferFrom(address from, address to, uint tokens) public returns (bool success) {
        if (balances[from] >= tokens && allowed[from][msg.sender] >= tokens && tokens > 0) {
            balances[from] = balances[from].sub(tokens);
            allowed[from][msg.sender] = allowed[from][msg.sender].sub(tokens);
            balances[to] = balances[to].add(tokens);
            emit Transfer(from, to, tokens);
            return true;
        } else { return false; }
    }


    // ------------------------------------------------------------------------
    // Returns the amount of tokens approved by the owner that can be
    // transferred to the spender's account
    // ------------------------------------------------------------------------
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining) {
        return allowed[tokenOwner][spender];
    }
    

   /**
   * @dev Burns a specific amount of tokens.
   * @param _value The amount of token to be burned.
   */
  function burn(uint256 _value) onlyOwner public {
      require(_value > 0);
      require(_value <= balances[msg.sender]);
      address burner = msg.sender;
      balances[burner] = balances[burner].sub(_value);
      _totalSupply = _totalSupply.sub(_value);
      emit Burn(burner, _value);
      emit Transfer(burner, address(0), _value);
  }
  
}