// File: Address.sol



pragma solidity 0.8.10;
// SPDX-License-Identifier: UNLICENSED
/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
}
// File: IERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)

pragma solidity 0.8.10;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) external returns (bool);
}
// File: meme-szn.sol



// SPDX-License-Identifier: Unlicensed
//meme-szn.sol

//███╗░░░███╗███████╗███╗░░░███╗███████╗░██████╗███████╗███╗░░██╗
//████╗░████║██╔════╝████╗░████║██╔════╝██╔════╝╚════██║████╗░██║
//██╔████╔██║█████╗░░██╔████╔██║█████╗░░╚█████╗░░░███╔═╝██╔██╗██║
//██║╚██╔╝██║██╔══╝░░██║╚██╔╝██║██╔══╝░░░╚═══██╗██╔══╝░░██║╚████║
//██║░╚═╝░██║███████╗██║░╚═╝░██║███████╗██████╔╝███████╗██║░╚███║
//╚═╝░░░░░╚═╝╚══════╝╚═╝░░░░░╚═╝╚══════╝╚═════╝░╚══════╝╚═╝░░╚══╝

pragma solidity 0.8.10;

import "./SafeMath.sol";
import "./IERC20.sol";
import "./Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for ERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */

library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves.

        // A Solidity high level call has three parts:
        //  1. The target address is checked to verify it contains contract code
        //  2. The call itself is made, and success asserted
        //  3. The return value is decoded, which in turn checks the size of the returned data.
        // solhint-disable-next-line max-line-length
        require(address(token).isContract(), "SafeERC20: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = address(token).call(data);
        require(success, "SafeERC20: low-level call failed");

        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

////////////////////////////////////////////////
////////////////////EVENTS/////////////////////
//////////////////////////////////////////////

contract TokenEvents {
    
    //when a user stakes tokens
    event TokenStake(
        address indexed user,
        uint value
    );

    //when a user unstakes tokens
    event TokenUnstake(
        address indexed user,
        uint value
    );
    
    //when a user burns tokens
    event TokenBurn(
        address indexed user,
        uint value
    );
    
}

//////////////////////////////////////
//////////MEMESZN TOKEN CONTRACT////////
////////////////////////////////////
contract MEMESZN is IERC20, TokenEvents {

    using SafeMath for uint256;
    using SafeMath for uint64;
    using SafeMath for uint32;
    using SafeMath for uint16;
    using SafeMath for uint8;

    using SafeERC20 for MEMESZN;
    
    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    //stake setup
    uint constant internal MINUTESECONDS = 60;
    uint constant internal DAYSECONDS = 86400;
    uint constant internal MINSTAKEDAYLENGTH = 7;
    uint256 public totalStaked;
    uint256 public totalBurned;
    //tokenomics
    uint256 internal _totalSupply;
    string public constant name = "memeszn";
    string public constant symbol = "MEME";
    uint8 public constant decimals = 18;

    bool private sync;
    
    mapping (address => Staker) public staker;
    
    struct Staker{
        uint256 stakedBalance;
        uint256 stakeStartTimestamp;
        uint256 totalStakingInterest;
        uint256 totalBurnt;
        uint256 totalReferralBonus;
        address referrer;
        bool activeUser;
    }
    
    //protects against potential reentrancy
    modifier synchronized {
        require(!sync, "Sync lock");
        sync = true;
        _;
        sync = false;
    }

    constructor(uint256 initialTokens) {
        _mint(msg.sender, initialTokens);
    }

    
    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() external view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) external override returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) external view override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) external override returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for `sender`'s tokens of at least
     * `amount`.
     */
     
    function transferFrom(address sender, address recipient, uint256 amount) external override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) external returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) external returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");
        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply unless mintBLock is true
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal {
        uint256 amt = amount;
        require(account != address(0), "ERC20: mint to the zero address");
        _totalSupply = _totalSupply.add(amt);
        _balances[account] = _balances[account].add(amt);
        emit Transfer(address(0), account, amt);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: burn from the zero address");
        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`.`amount` is then deducted
     * from the caller's allowance.
     *
     * See {_burn} and {_approve}.
     */
    function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(account, msg.sender, _allowances[account][msg.sender].sub(amount, "ERC20: burn amount exceeds allowance"));
    }

    ////////////////////////////////////////////////////////
    /////////////////PUBLIC FACING - MEME CONTROL//////////
    //////////////////////////////////////////////////////
    
    
    ////////STAKING FUNCTIONS/////////
    
    //stake MEME tokens to contract and claims any accrued interest
    function StakeTokens(uint amt, address _referrer)
        external
        synchronized
    {
        require(amt > 0, "zero input");
        require(memeBalance() >= amt, "Error: insufficient balance");//ensure user has enough funds
        if(_referrer != address(0) && _referrer != msg.sender){
            if(staker[_referrer].activeUser && staker[msg.sender].referrer == address(0)){
               staker[msg.sender].referrer = _referrer;
            }
        }
        //claim any accrued interest
        claimInterest();
        //update balances
        staker[msg.sender].activeUser = true;
        staker[msg.sender].stakedBalance = staker[msg.sender].stakedBalance.add(amt);
        totalStaked = totalStaked.add(amt);
        _transfer(msg.sender, address(this), amt);//make transfer
        emit TokenStake(msg.sender, amt);
    }
    
    //unstake MEME tokens from contract and claims any accrued interest
    function UnstakeTokens()
        external
        synchronized
    {
        require(staker[msg.sender].stakedBalance > 0,"Error: unsufficient staked balance");//ensure user has enough staked funds
        require(isStakeFinished(msg.sender), "tokens cannot be unstaked yet. min 7 day stake");
        uint amt = staker[msg.sender].stakedBalance;
        //claim any accrued interest
        claimInterest();
        //zero out staking timestamp
        staker[msg.sender].stakeStartTimestamp = 0;
        staker[msg.sender].stakedBalance = 0;
        totalStaked = totalStaked.sub(amt);
        _transfer(address(this), msg.sender, amt);//make transfer
        emit TokenUnstake(msg.sender, amt);
    }
    
    //claim any accrued interest
    function ClaimStakeInterest()
        external
        synchronized
    {
        require(staker[msg.sender].stakedBalance > 0, "you have no staked balance");
        claimInterest();
    }
    
    //roll any accrued interest
    function RollStakeInterest()
        external
        synchronized
    {
        require(staker[msg.sender].stakedBalance > 0, "you have no staked balance");
        rollInterest();
    }
    
    function rollInterest()
        internal
    {
        //calculate staking interest
        uint256 interest = calcStakingRewards(msg.sender);
        //mint interest to contract, ref and devs
        if(interest > 0){
            _mint(address(this), interest);
            //roll interest
            staker[msg.sender].stakedBalance = staker[msg.sender].stakedBalance.add(interest);
            totalStaked = totalStaked.add(interest);
            staker[msg.sender].totalStakingInterest += interest;
            //reset staking timestamp
            staker[msg.sender].stakeStartTimestamp = block.timestamp;
            if(staker[msg.sender].referrer != address(0)){
                 _mint(staker[msg.sender].referrer, interest.div(20));//5% bonus for referrer
                 staker[staker[msg.sender].referrer].totalReferralBonus += interest.div(20);
            }
        }
    }
    
    function claimInterest()
        internal
    {
        //calculate staking interest
        uint256 interest = calcStakingRewards(msg.sender);
        //reset staking timestamp
        staker[msg.sender].stakeStartTimestamp = block.timestamp;
        //mint interest if any
        if(interest > 0){
            _mint(msg.sender, interest);
            staker[msg.sender].totalStakingInterest += interest;
            if(staker[msg.sender].referrer != address(0)){
                 _mint(staker[msg.sender].referrer, interest.div(20));//5% bonus for referrer
                 staker[staker[msg.sender].referrer].totalReferralBonus += interest.div(20);
            }
        }
    }

    //burn meme to increase staking APY to maximum 10x @ 42% APY
    function BurnMeme(uint amt)
        external
        synchronized
    {
        require(amt > 0, "value must be greater than 0");
        require(balanceOf(msg.sender) >= amt, "balance too low");
        //burn tokens of user
        _burn(msg.sender, amt);
        staker[msg.sender].totalBurnt += amt;
        totalBurned += amt;
        _totalSupply = _totalSupply.sub(amt);
        emit TokenBurn(msg.sender, amt);
    }

    ///////////////////////////////
    ////////VIEW ONLY//////////////
    ///////////////////////////////

    //returns staking rewards in MEME
    function calcStakingRewards(address _user)
        public
        view
        returns(uint)
    {
        // totalstaked * minutesPast / 10000 / 1251 @ 4.20% APY
        // (adjustments up to a max of 42.0% APY via burning of MEME)
        uint memeBurnt = staker[_user].totalBurnt;
        uint staked = staker[_user].stakedBalance;
        uint apyAdjust = 10000;
        if(memeBurnt > 0){
            if(memeBurnt >= staked.sub(staked.div(10)))
            {
                apyAdjust = 1000;
            }
            else{
                uint burntPercentage = ((memeBurnt.mul(100) / staked));
                uint v = (apyAdjust * burntPercentage) / 100;
                apyAdjust = apyAdjust.sub(v);
                if(apyAdjust < 1000)
                {
                    apyAdjust = 1000;
                }
            }
        }
        return (staked.mul(minsPastStakeTime(_user)).div(apyAdjust).div(1251));
    }

    //returns amount of minutes past since stake start
    function minsPastStakeTime(address _user)
        public
        view
        returns(uint)
    {
        if(staker[_user].stakeStartTimestamp == 0){
            return 0;
        }
        uint minsPast = block.timestamp.sub(staker[_user].stakeStartTimestamp).div(MINUTESECONDS);
        if(minsPast >= 1){
            return minsPast;// returns 0 if under 1 min passed
        }
        else{
            return 0;
        }
    }
    
    //check is stake is finished, min 7 days
    function isStakeFinished(address _user)
        public
        view
        returns(bool)
    {
        if(staker[_user].stakeStartTimestamp == 0){
            return false;
        }
        else{
            return staker[_user].stakeStartTimestamp.add((DAYSECONDS).mul(MINSTAKEDAYLENGTH)) <= block.timestamp;             
        }
    }

    //MEME balance of caller
    function memeBalance()
        public
        view
        returns (uint256)
    {
        return balanceOf(msg.sender);
    }
}

// File: SafeMath.sol



pragma solidity 0.8.10;
// SPDX-License-Identifier: UNLICENSED
/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot 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-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}