Twitter getting added to S&P 500; Stock jumps 4% afterhours

Huh. Cliffs are real.

I want an index that invests in the 11th, 21st, 51st, 101st, 501st, and 1001st largest companies, betting that they are probably undervalued for falling just outside some arbitrary range.

(Or that random mergers might give them all spontaneous bumps.)