    function unregister(IAsset asset) external governance {
        require(_erc20s.contains(address(asset.erc20())), "no asset to unregister");
        require(assets[asset.erc20()] == asset, "asset not found");
        uint192 quantity = basketHandler.quantity(asset.erc20());

        _erc20s.remove(address(asset.erc20()));
        assets[asset.erc20()] = IAsset(address(0));
        emit AssetUnregistered(asset.erc20(), asset);

        if (quantity > 0) basketHandler.disableBasket();
    }
    function quantity(IERC20 erc20) public view returns (uint192) {
        try assetRegistry.toColl(erc20) returns (ICollateral coll) {
            if (coll.status() == CollateralStatus.DISABLED) return FIX_ZERO;

            uint192 refPerTok = coll.refPerTok(); // {ref/tok}
            if (refPerTok > 0) {
                // {tok/BU} = {ref/BU} / {ref/tok}
                return basket.refAmts[erc20].div(refPerTok, CEIL);
            } else {
                return FIX_MAX;
            }
        } catch {
            return FIX_ZERO;
        }
    }
    function refPerTok() public view override returns (uint192) {
        uint256 rate = ICToken(address(erc20)).exchangeRateStored();
        int8 shiftLeft = 8 - int8(referenceERC20Decimals) - 18;
        return shiftl_toFix(rate, shiftLeft);
    }
    function refresh() public virtual override {
        // == Refresh ==
        // Update the Compound Protocol
        ICToken(address(erc20)).exchangeRateCurrent();

        // Intentional and correct for the super call to be last!
        super.refresh(); // already handles all necessary default checks
    }
    function refresh() public {
        // It's a waste of gas to require notPausedOrFrozen because assets can be updated directly
        uint256 length = _erc20s.length();
        for (uint256 i = 0; i < length; ++i) {
            assets[IERC20(_erc20s.at(i))].refresh();
        }
    }
