function createTradeContract(       
        address _asset, 
        uint256 _sellPrice, 
        uint256 _units,
        bool    _sellsTokens
        ) returns (address) 
    {
        if(_units == 0) throw;              

        address trader = new TokenTrader (
                     _asset, 
                     _sellPrice, 
                     _units,
                     _sellsTokens);

        var bookid = sha3(_asset,_units);

        _verify[trader] = true; 

        TokenTrader(trader).transferOwnership(msg.sender); 

        if(pairExits[bookid] == false) {
            pairExits[bookid] = true;
            NewBook(bookid, _asset, _units);
        }

        TradeListing(bookid,msg.sender,trader);
    }