function withdraw(address _usdcVersion, uint256 _amount) external returns (uint256) {
    // check whitelist
    require(whitelistedUSDCVersions[_usdcVersion], "ASDUSDC: USDC version not whitelisted");  // @audit owner can block withdrawals
    // burn tokens
    _burn(msg.sender, _amount);
    // calculate amount to withdraw
    uint256 amountToWithdraw = _amount / (10 ** (this.decimals() - ERC20(_usdcVersion).decimals()));
    // check balance
    require(usdcBalances[_usdcVersion] >= amountToWithdraw, "ASDUSDC: Not enough USDC balance");
    // transfer USDC
    usdcBalances[_usdcVersion] -= amountToWithdraw;
    SafeERC20.safeTransfer(ERC20(_usdcVersion), msg.sender, amountToWithdraw);
    emit Withdrawal(_usdcVersion, amountToWithdraw);
    return amountToWithdraw;
}
