Can you solve the time travel riddle? - Dan Finkel

3,438,225 views ใƒป 2018-12-04

TED-Ed


ืื ื ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ืœืžื˜ื” ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ.

ืชืจื’ื•ื: Ido Dekkers ืขืจื™ื›ื”: Allon Sasson
00:07
Your internship in Professor Ramseyโ€™s physics lab has been amazing.
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ื”ื”ืชืžื—ื•ืช ืฉืœื›ื ื‘ืžืขื‘ื“ืช ื”ืคื™ื–ื™ืงื” ืฉืœ ืคืจื•ืคืกื•ืจ ืจืžื–ื™ ื”ื™ืชื” ืžื“ื”ื™ืžื”.
00:11
Until, that is, the professor accidentally stepped through a time portal.
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ืขื“, ื›ืžื•ื‘ืŸ, ืฉื”ืคืจื•ืคืกื•ืจ ืฆืขื“ ื‘ื˜ืขื•ืช ื“ืจืš ืฉืขืจ ื–ืžืŸ.
00:16
Youโ€™ve got just a minute to jump through the portal to save him before it closes
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ื™ืฉ ืœื›ื ืจืง ื“ืงื” ืœืงืคื•ืฅ ื“ืจืš ื”ืคื•ืจื˜ืœ ื›ื“ื™ ืœื”ืฆื™ืœ ืื•ืชื• ืœืคื ื™ ืฉื™ื™ืกื’ืจ
00:20
and leaves him stranded in history.
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ื•ื™ืฉืื™ืจ ืื•ืชื• ืชืงื•ืข ื‘ื”ื™ืกื˜ื•ืจื™ื”.
00:23
Once youโ€™re through it, the portal will close,
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ื‘ืจื’ืข ืฉืชืขื‘ืจื• ื“ืจื›ื•,
ื”ืคื•ืจื˜ืœ ื™ื™ืกื’ืจ, ื•ื”ื“ืจืš ื”ื™ื—ื™ื“ื” ืฉืœื›ื ื—ื–ืจื” ืชื”ื™ื” ืœื™ืฆื•ืจ ืื—ื“ ื—ื“ืฉ
00:25
and your only way back will be to create a new one
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00:29
using the chrono-nodules from your lab.
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ืชื•ืš ืฉื™ืžื•ืฉ ื‘ืงึดืฉืึฐืจึดื™ืจื™ื•ืช ื”ื›ืจื•ื ื• ืžื”ืžืขื‘ื“ื” ืฉืœื›ื.
00:32
Activated nodules connect to each other
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ืงืฉืจื™ืจื™ื•ืช ืžื•ืคืขืœื•ืช ืžืชื—ื‘ืจื•ืช ืื—ืช ืœืฉื ื™ื”
00:34
via red or blue tachyon entanglement.
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ื“ืจืš ืกื™ื‘ื•ื›ื™ื•ืช ื˜ืื›ื™ื•ื ื™ื ืื“ื•ืžื” ืื• ื›ื—ื•ืœื”.
00:38
Activate more nodules and theyโ€™ll connect
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ื”ืคืขื™ืœื• ื™ื•ืชืจ ืงืฉืจื™ืจื™ื•ืช ื•ื”ืŸ ื™ืชื—ื‘ืจื•
00:40
to all other nodules in the area.
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ืœื›ืœ ื”ืงืฉืจื™ืจื™ื•ืช ื”ืื—ืจื•ืช ื‘ืื–ื•ืจ.
00:43
As soon as a red or blue triangle is created with a nodule at each point,
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ื‘ืจื’ืข ืฉืžืฉื•ืœืฉ ืื“ื•ื ืื• ื›ื—ื•ืœ ื ื•ืฆืจ ืขื ืงืฉืจื™ืจื™ืช ื‘ื›ืœ ื ืงื•ื“ื”,
00:48
it opens a doorway through time that will take you back to the present.
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ื”ื•ื ืคื•ืชื— ืคืชื— ื“ืจืš ื”ื–ืžืŸ ืฉื™ืงื— ืืชื›ื ื—ื–ืจื” ืœื”ื•ื•ื”.
00:53
But the color of each individual connection manifests at random,
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ืื‘ืœ ื”ืฆื‘ืข ืฉืœ ื›ืœ ื—ื™ื‘ื•ืจ ื‘ื•ื“ื“ ืžืชื’ืฉื ื‘ืืงืจืื™ื•ืช,
00:58
and thereโ€™s no way to choose or change its color.
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ื•ืื™ืŸ ื“ืจืš ืœื‘ื—ื•ืจ ืื• ืœืฉื ื•ืช ืืช ืฆื‘ืขื•.
01:02
And thereโ€™s one more problem:
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ื•ื™ืฉ ืขื•ื“ ื‘ืขื™ื”:
01:03
each individual nodule creates a temporal instability
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ื›ืœ ืงืฉืจื™ืจื™ืช ื‘ื•ื“ื“ืช ื™ื•ืฆืจืช ื—ื•ืกืจ ื™ืฆื™ื‘ื•ืช ื–ืžื ื™ืช
01:08
that raises the chances the portal might collapse as you go through it.
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ืฉืžืขืœื” ืืช ื”ืกื™ื›ื•ื™ ืฉื”ืคื•ืจื˜ืœ ื™ืงืจื•ืก ื›ืฉืืชื ืขื•ื‘ืจื™ื ื“ืจื›ื•.
01:12
So the fewer you bring, the better.
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ืื– ื›ื›ืœ ืฉืชื‘ื™ืื• ืคื—ื•ืช, ื™ื•ืชืจ ื˜ื•ื‘.
01:15
The portalโ€™s about to close.
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ื”ืคื•ืจื˜ืœ ืขื•ืžื“ ืœื”ืกื’ืจ.
01:17
Whatโ€™s the minimum number of nodules you need to bring
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ืžื” ื”ืžืกืคืจ ื”ืžื™ื ื™ืžืœื™ ืฉืœ ืงืฉืจื™ืจื™ื•ืช ืฉืืชื ืฆืจื™ื›ื™ื ืœื”ื‘ื™ื ื›ื“ื™ ืœื”ื™ื•ืช ื‘ื˜ื•ื—ื™ื
01:20
to be certain youโ€™ll create a red or blue triangle and get back to the present?
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ืฉืชืฆืจื• ืžืฉื•ืœืฉ ืื“ื•ื ืื• ื›ื—ื•ืœ ื•ืœื—ื–ื•ืจ ืœื”ื•ื•ื”?
01:24
Pause here if you want to figure it out for yourself!
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ืขืฆืจื• ืคื” ืื ืืชื ืจื•ืฆื™ื ืœื’ืœื•ืช ื‘ืขืฆืžื›ื!
01:29
Answer in: 3
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ืชืฉื•ื‘ื” ืขื•ื“ 3
01:31
Answer in: 2
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ืชืฉื•ื‘ื” ืขื•ื“ 2
01:33
Answer in: 1
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ืชืฉื•ื‘ื” ืขื•ื“ 1
01:34
This question is so rich that an entire branch of mathematics
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ื”ืฉืืœื” ื›ืœ ื›ืš ืขืฉื™ืจื” ืฉืขื ืฃ ืฉืœื ืฉืœ ืžืชืžื˜ื™ืงื”
01:38
known as Ramsey Theory developed from it.
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ืฉื™ื“ื•ืข ื›ืชืื•ืจื™ืช ืจืืžื–ื™ ืคื•ืชื— ืžืžื ื•.
01:41
Ramsey Theory is home to some famously difficult problems.
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ืชืื•ืจื™ื™ืช ืจืืžื–ื™ ื”ื™ื ื‘ื™ืช ืœื›ืžื” ื‘ืขื™ื•ืช ืงืฉื•ืช ื‘ืื•ืคืŸ ืžืคื•ืจืกื.
01:45
This one isnโ€™t easy, but it can be handled
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ื–ื• ืœื ืงืœื”, ืื‘ืœ ืืคืฉืจ ืœื”ืชืžื•ื“ื“ ืื™ืชื”
01:48
if you approach it systematically.
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ืื ืืชื ื ื™ื’ืฉื™ื ืืœื™ื” ื‘ืื•ืคืŸ ืกื“ื•ืจ.
01:50
Imagine you brought just three nodules.
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ื“ืžื™ื™ื ื• ืฉื”ื‘ืืชื ืจืง ืฉืœื•ืฉ ืงืฉืจื™ืจื™ื•ืช.
01:53
Would that be enough? No - for example, you might have two blue
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ื”ืื ื–ื” ื™ื”ื™ื” ืžืกืคื™ืง? ืœื - ืœื“ื•ื’ืžื”, ืื•ืœื™ ื™ื”ื™ื• ืœื›ื ืฉื ื™ ื—ื™ื‘ื•ืจื™ื ื›ื—ื•ืœื™ื
01:57
and one red connection, and be stuck in the past forever.
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ื•ืื“ื•ื ืื—ื“, ื•ืชื”ื™ื• ืชืงื•ืขื™ื ื‘ืขื‘ืจ ืœืขื“.
02:01
Would four nodules be enough? No - there are many arrangements here
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ื”ืื ืืจื‘ืข ืงืฉืจื™ืจื™ื•ืช ื™ื”ื™ื• ืžืกืคื™ืง? ืœื - ื™ืฉ ื”ืจื‘ื” ืกื™ื“ื•ืจื™ื ืคื”
02:06
that donโ€™t give a blue or red triangle.
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ืฉืœื ื ื•ืชื ื™ื ืžืฉื•ืœืฉ ื›ื—ื•ืœ ืื• ืื“ื•ื.
02:09
What about five?
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ืžื” ืขื ื—ืžื™ืฉื”? ืžืกืชื‘ืจ
02:10
It turns out there is an arrangement of connections
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ืฉื™ืฉ ืกื™ื“ื•ืจ ืฉืœ ื—ื™ื‘ื•ืจื™ื ืฉื ืžื ืข ืžืœื™ืฆื•ืจ ืžืฉื•ืœืฉ ืื“ื•ื ืื• ื›ื—ื•ืœ.
02:13
that avoids creating a blue or red triangle.
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02:16
These smaller triangles donโ€™t count because they donโ€™t have a nodule at each corner.
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ื”ืžืฉื•ืœืฉื™ื ื”ืงื˜ื ื™ื ื™ื•ืชืจ ืœื ื ื—ืฉื‘ื™ื ื‘ื’ืœืœ ืฉืื™ืŸ ืœื”ื ืงืฉืจื™ืจื™ืช ื‘ื›ืœ ืคื™ื ื”.
02:22
However, six nodules will always create a blue triangle or a red triangle.
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ืขื ื–ืืช, ืฉืฉ ืงืฉืจื™ืจื™ื•ืช ืชืžื™ื“ ื™ืฆืจื• ืžืฉื•ืœืฉ ื›ื—ื•ืœ ืื• ืื“ื•ื.
02:28
Hereโ€™s how we can prove that without sorting through every possible case.
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ื›ืš ืืชื ื™ื›ื•ืœื™ื ืœื”ื•ื›ื™ื— ื‘ืœื™ ืœืขื‘ื•ืจ ืขืœ ื›ืœ ืžืงืจื” ืืคืฉืจื™.
02:32
Imagine activating the sixth nodule,
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ื“ืžื™ื™ื ื• ืฉืืชื ืžืคืขื™ืœื™ื ืืช ื”ืงืฉืจื™ืจื™ืช ื”ืฉื™ืฉื™ืช, ื•ืฉืงืœื• ืื™ืš ื”ื™ื ืชืชื—ื‘ืจ
02:35
and consider how it might connect to the other five.
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ืœื—ืžืฉ ื”ืื—ืจื•ืช. ื”ื™ื ื™ื›ื•ืœื” ืœืขืฉื•ืช ื–ืืช ื‘ืื—ืช ืžืฉืฉ ื“ืจื›ื™ื:
02:38
It could do so in one of six ways:
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02:41
with five red connections, five blue connections, or some mix of red and blue.
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ืขื ื—ืžื™ืฉื” ื—ื™ื‘ื•ืจื™ื ืื“ื•ืžื™ื, ื—ืžื™ืฉื” ื—ื™ื‘ื•ืจื™ื ื›ื—ื•ืœื™ื, ืื• ืขื™ืจื•ื‘ ื›ืœืฉื”ื• ืฉืœ ืื“ื•ื ื•ื›ื—ื•ืœ.
02:46
Notice that every possibility has at least three connections of the same color
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ืฉื™ืžื• ืœื‘ ืฉืœื›ืœ ืืคืฉืจื•ืช ื™ืฉ ืœืคื—ื•ืช
ืฉืœื•ืฉื” ื—ื™ื‘ื•ืจื™ื ื‘ืื•ืชื• ืฆื‘ืข ืฉืžื’ื™ืขื™ื ืžื”ืงืฉืจื™ืจื™ืช ื”ื–ื•.
02:51
coming from this nodule.
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02:53
Letโ€™s look at just the nodules on the other end
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ื‘ื•ืื• ื ื‘ื™ื˜ ืจืง ืขืœ ืงืฉืจื™ืจื™ืช ืื—ืช ื‘ืงืฆื” ื”ืฉื ื™
02:56
of those same three color connections.
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ืฉืœ ืื•ืชื ืฉืœื•ืฉื” ื—ื™ื‘ื•ืจื™ื ืฆื‘ืขื•ื ื™ื™ื. ืื ื”ื—ื™ื‘ื•ืจื™ื ื”ื™ื• ื›ื—ื•ืœื™ื,
02:58
If the connections were blue,
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03:00
then any additional blue connection between those three would give us a blue triangle.
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ืื– ื›ืœ ื—ื™ื‘ื•ืจ ื›ื—ื•ืœ ื ื•ืกืฃ ื‘ื™ืŸ ืฉืœื•ืฉืช ืืœื”
ื™ืชืŸ ืœื ื• ืžืฉื•ืœืฉ ื›ื—ื•ืœ.
03:05
So the only way we could get in trouble
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ืื– ื”ื“ืจืš ื”ื™ื—ื™ื“ื” ืฉื ื•ื›ืœ ืœื”ืกืชื‘ืš
03:07
is if all the connections between them were red.
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ื”ื™ื ืื ื›ืœ ื”ื—ื™ื‘ื•ืจื™ื ื‘ื™ื ื ื™ื”ื™ื• ืื“ื•ืžื™ื.
03:10
But those three red connections would give us a red triangle.
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ืื‘ืœ ืฉืœื•ืฉืช ื”ื—ื™ื‘ื•ืจื™ื ื”ืื“ื•ืžื™ื ื”ืืœื• ื™ืชื ื• ืœื ื• ืžืฉื•ืœืฉ ืื“ื•ื.
03:14
No matter what happens, weโ€™ll get a red or a blue triangle,
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ืœื ืžืฉื ื” ืžื” ื™ืงืจื”, ื ืงื‘ืœ ืžืฉื•ืœืฉ ืื“ื•ื ืื• ื›ื—ื•ืœ,
03:18
and open our doorway.
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ื•ื ืคืชื— ืืช ื”ืžืขื‘ืจ ืฉืœื ื•.
03:20
On the other hand,
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ืžืฆื“ ืฉื ื™, ืื ื›ืœ ืฉืœื•ืฉืช ื”ื—ื™ื‘ื•ืจื™ื ื”ืžืงื•ืจื™ื™ื
03:21
if the original three connections were all red instead of blue,
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ื”ื™ื• ืื“ื•ืžื™ื ื‘ืžืงื•ื ื›ื—ื•ืœื™ื, ืื•ืชื• ื˜ืขื•ืŸ ืขื“ื™ื™ืŸ ืขื•ื‘ื“,
03:25
the same argument still works, with all the colors flipped.
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ืขืœ ื›ืœ ื”ืฆื‘ืขื™ื ื”ืคื•ื›ื™ื.
03:29
In other words, no matter how the connections are colored,
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ื‘ืžื™ืœื™ื ืื—ืจื•ืช, ืœื ืžืฉื ื” ืื™ืš ื”ื—ื™ื‘ื•ืจื™ื ืฆื‘ื•ืขื™ื,
ืฉืฉ ืงืฉืจื™ืจื™ื•ืช ืชืžื™ื“ ื™ื™ืฆืจื• ืžืฉื•ืœืฉ ืื“ื•ื ืื• ื›ื—ื•ืœ
03:32
six nodules will always create a red or blue triangle and a doorway leading home.
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ื•ื“ืœืช ืฉืžื•ื‘ื™ืœื” ื”ื‘ื™ืชื”.
03:38
So you grab six nodules and jump through the portal.
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ืื– ืืชื ืœื•ืงื—ื™ื ืฉืฉ ืงืฉืจื™ืจื™ื•ืช ื•ืงื•ืคืฆื™ื ื“ืจืš ื”ืคื•ืจื˜ืœ.
03:41
You were hoping your internship would give you valuable life experience.
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ืงื™ื•ื•ื™ืชื ืฉื”ื”ืชืžื—ื•ืช ืชืชืŸ ืœื›ื ื—ื•ื•ื™ื•ืช ื—ื™ื™ื ื‘ืขืœื•ืช ืขืจืš.
03:45
Turns out, that didnโ€™t take much time.
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ืžืกืชื‘ืจ ืฉื–ื” ืœื ืœืงื— ื”ืจื‘ื” ื–ืžืŸ.
ืขืœ ืืชืจ ื–ื”

ืืชืจ ื–ื” ื™ืฆื™ื’ ื‘ืคื ื™ื›ื ืกืจื˜ื•ื ื™ YouTube ื”ืžื•ืขื™ืœื™ื ืœืœื™ืžื•ื“ ืื ื’ืœื™ืช. ืชื•ื›ืœื• ืœืจืื•ืช ืฉื™ืขื•ืจื™ ืื ื’ืœื™ืช ื”ืžื•ืขื‘ืจื™ื ืขืœ ื™ื“ื™ ืžื•ืจื™ื ืžื”ืฉื•ืจื” ื”ืจืืฉื•ื ื” ืžืจื—ื‘ื™ ื”ืขื•ืœื. ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ื”ืžื•ืฆื’ื•ืช ื‘ื›ืœ ื“ืฃ ื•ื™ื“ืื• ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ ืžืฉื. ื”ื›ืชื•ื‘ื™ื•ืช ื’ื•ืœืœื•ืช ื‘ืกื ื›ืจื•ืŸ ืขื ื”ืคืขืœืช ื”ื•ื•ื™ื“ืื•. ืื ื™ืฉ ืœืš ื”ืขืจื•ืช ืื• ื‘ืงืฉื•ืช, ืื ื ืฆื•ืจ ืื™ืชื ื• ืงืฉืจ ื‘ืืžืฆืขื•ืช ื˜ื•ืคืก ื™ืฆื™ืจืช ืงืฉืจ ื–ื”.

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