WHAT ARE EXCHANGE-TRADED NOTES?IPATH S&P 500 VIX SHORT-TERM FUTURES ETNIPATH S&P 500 VIX MID-TERM FUTURES ETNCOMPARING THE VXX AND VXZ PERFORMANCEBARCLAYS ETN+ INVERSE S&P 500 VIX SHORT-TERM FUTURES ETNBARCLAYS ETN+ S&P VEQTOR ETNS&P 500 VIX FUTURES SOURCE ETF