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Seems like you can just pre-announce any information source you do not control and then take hash mod 20 once the content is made available.

Ex.

- Next article title posted on NYT

- Donald Trumps next tweet

- Sum of tomorrow's lottery numbers, mod 20

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But that means waiting for the third party right?

You can use publicly available data feeds that changes every few minutes. For example, CNN's Afterhours trading data [0] seems to work pretty well. And it's just HTML, so you just hash it and you're good.

[0] http://money.cnn.com/data/afterhours/

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