Among the largest underlying components of PDP, in trading today Liberty Media Corporation ( NASD: LCAPA) is up about 0.9%, Las Vegas Sands Corporation ( NYSE: LVS) is down about 0.5%, and Ralph Lauren Corporation ( NYSE: RL) is higher by about 0.7%.

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Armstrong has talked about adding other kinds of tracking shares but so far has carved out only Liberty Media for separate trading.

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