Warum werden Fehler in diesem Vertrag angezeigt?

Eigentlich habe ich den Code in mehrere Dateien geschrieben, aber da ich den Code verifizieren und veröffentlichen muss, habe ich versucht, den Code zu verflachen. Aber jetzt zeigt es viel zu viele Fehler. Ich habe den folgenden Code mit Fehlermeldungen in Kommentare eingefügt. Können Sie mir bitte bei den Fehlern helfen?

pragma solidity 0.4.25;

library SafeMath {

/**
* @dev Multiplies two numbers, reverts on overflow.
*/
function mul(uint256 a, uint256 b) internal pure returns (uint256) {
// Gas optimization: this is cheaper than requiring 'a' not being zero, but the
// benefit is lost if 'b' is also tested.
// See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
if (a == 0) {
  return 0;
}

uint256 c = a * b;
require(c / a == b);

return c;
}

/**
* @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
*/
function div(uint256 a, uint256 b) internal pure returns (uint256) {
require(b > 0); // Solidity only automatically asserts when dividing by 0
uint256 c = a / b;
// assert(a == b * c + a % b); // There is no case in which this doesn't hold

return c;
}

 /**
 * @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
 */
 function sub(uint256 a, uint256 b) internal pure returns (uint256) {
require(b <= a);
uint256 c = a - b;

return c;
}

/**
* @dev Adds two numbers, reverts on overflow.
*/
function add(uint256 a, uint256 b) internal pure returns (uint256) {
uint256 c = a + b;
require(c >= a);

return c;
}

/**
* @dev Divides two numbers and returns the remainder (unsigned integer modulo),
* reverts when dividing by zero.
*/
 function mod(uint256 a, uint256 b) internal pure returns (uint256) {
require(b != 0);
return a % b;
}
}


interface IERC20{        
function totalSupply() constant returns (uint256 totalSupply);
/**browser/ballot.sol:65:46: Warning: This declaration shadows an existing declaration.
function totalSupply() constant returns (uint256 totalSupply);
                                         ^-----------------^
browser/ballot.sol:65:5: The shadowed declaration is here:
function totalSupply() constant returns (uint256 totalSupply);
^------------------------------------------------------------^
**/
function balanceOf(address _owner) constant returns (uint256 balance);
function transfer(address _to, uint256 _value) returns (bool success);
function transferFrom(address _from, address _to, uint256 _value) returns (bool success);
function approve(address _spender, uint256 _value) returns (bool success);
function allowance(address _owner, address _spender) constant returns (uint256 remaining);
event Transfer(address indexed _from, address indexed _to, uint256 _value);
event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}

contract FuncToken is IERC20{

using SafeMath for uint256;

uint public constant _totalSupply = 0;

string public constant symbol = "UB";
string public constant name = "UNIFIED BET";
uint8 public constant decimals = 18;

//1 ether = 1 UB
uint256 public constant RATE = 1;

address public owner;

mapping (address => uint256) balances;
mapping (address => mapping(address => uint256)) allowed;

function () payable{
    createToken();
}

constructor (){
    owner = msg.sender;

}

function createToken() payable {
    require(msg.value > 0);

    uint256 tokens = msg.value;
    balances[msg.sender] = balances[msg.sender].add(tokens);

    owner.transfer(msg.value);
}

function totalSupply() constant returns (uint256 totalSupply){
    return _totalSupply;
}

function balanceOf(address _owner) constant returns (uint256 balance){
    return balances[_owner];
}

function transfer(address _to, uint256 _value) returns (bool success){
    require (
        balances[msg.sender] >= _value
        && _value > 0
        );
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        Transfer(msg.sender, _to, _value);
        /**browser/ballot.sol:126:13: Warning: Invoking events without "emit" prefix is deprecated.
        Transfer(msg.sender, _to, _value);
        ^-------------------------------^ **/
        return true;

}

function transferFrom(address _from, address _to, uint256 _value) returns (bool success){
    require(
        allowed[_from][msg.sender] >= _value
        && balances[_from] >= _value
        && _value > 0
        );

        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].add(_value);
        Transfer(_from, _to, _value);
        return true;
}

function approve(address _spender, uint256 _value) returns (bool success){
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
}

function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
    return allowed[_owner][_spender];
}

}

Jede Hilfe wird geschätzt. Es gibt mehr Fehler mit denselben Warnungen, aber wenn Sie mir einen mitteilen können, werde ich andere beheben. Alle Fehler sind in /** **/