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It was a normal Tuesday [br]at the superconductor,

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until a bug in the system created [br]a small situation.

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Now your team is trapped in eleven [br]separate pocket dimensions.

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Luckily for you, there’s a half-finished [br]experimental teleportation robot

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that may be able to get you all home,

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if you can figure out how to work through[br]the quirks of its design.

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Over interdimensional radio,

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your engineers explain

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that the robot can teleport into the [br]alternate universes you’re trapped in,

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but it’ll do so completely at random.

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The robot has two levers [br]and one big button.

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When it appears,

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you just switch the position of one [br]of the levers from A to B or vice versa,

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and then the robot will note your [br]dimensional position

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and teleport to another of the eleven [br]dimensions at random.

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If it shows up again, you’ll have to pull [br]a lever before it’ll teleport away.

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When anyone presses the button,

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the robot will bring everyone who pulled[br]a lever back home.

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Anyone who didn’t will be lost [br]in the multi-verse forever.

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The challenge is to make sure everyone[br]has pulled a lever

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before anyone hits the button.

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While you can talk to each other now[br]over the interdimensional radio

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and agree on a plan,

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the robot’s teleportation technology

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will interfere with all attempts [br]at communication once it arrives.

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You won’t be able to attach messages [br]to the robot

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or scratch notes into its superstrong[br]alloy body.

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Your only way to communicate information

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is to change the position of exactly [br]one lever or hit the button.

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What plan will make sure [br]everyone gets home?

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Pause the video now if you want to[br]figure it out for yourself.

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Answer in 3

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Answer in 2

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Answer in 1

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It would be nice if you could set [br]different combinations of the levers

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to indicate who’s already [br]been visited by the robot.

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But it has only two levers.

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That gives four combinations—

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far too few to communicate [br]about 11 people,

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especially when you’re forced to flip [br]one to send the robot onward.

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There must be another way.

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The critical insight is that not[br]everyone has to know

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when every pocket dimension[br]has been visited.

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If one person accepts responsibility [br]ahead of time for hitting the button,

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then only they need to know who the robot[br]has visited.

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In fact, they don’t even need to know [br]exactly who’s been visited…

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just how many people have been.

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You volunteer to be the person in charge [br]of pressing the button

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when the moment is right,

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and give the following directions[br]to everyone else.

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Your plan is simple:

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you’ll use the left lever to count visits,

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and the right lever will have no meaning,

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so there’s no harm in [br]moving it up or down.

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Each of the others will pull the left[br]lever

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from position A to position [br]B exactly once.

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If the robot appears with the left lever[br]already pulled down,

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or if an individual has previously pulled[br]the left lever down

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at any point in the past,

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then they should move the right lever.

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You, meanwhile, will be the only one who [br]ever resets the left lever from position B

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to position A.

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This gives you a way to count how many [br]people have been visited by the robot.

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Everyone needs to pull the left lever [br]down exactly once,

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and you’re the only one [br]to pull it back up.

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So you know that the tenth time [br]the robot visits you

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with its left lever in the down position,

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it must have visited [br]all ten of the others.

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And that means you’re safe to press the [br]button and teleport everyone home.

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It may take a while–

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most likely the robot will need to [br]teleport around 355 times;

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but better that than leave anyone behind.

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Your teammates phase back into your home[br]dimension one at a time.

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The mission proves a great success.

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Well...mostly.