Earthsky is a simple game where two players each throw a hand sign on the
count of three, and the winner is chosen based on who threw the superior sign.

To play, each player chooses one of the following signs with CHOOSE <SIGN>.
Each sign defeats two other specific signs, loses to two more, and ties with
itself:

* LIGHTNING: absorbs wind and shocks river. (One finger pointed down)
* WIND: directs river and carves mountain. (Palm forward, spread fingers)
* RIVER: erodes mountain and quenches flame (A flat hand, palm down)
* MOUNTAIN: stifles flame and grounds lightning (A closed fist)
* FLAME: feeds on lightning and wind (A cupped hand, palm up)

If a sign is not chosen quickly, the player will always show MOUNTAIN, as it
is the simplest sign to make with a hand.

The game ends after a best of 5 matches, with the winner being the player
who triumphed in 3 of those matches.

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