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I have time traveled to the past on an oriental country in southeast Asia. I want to hide my island from European colonists using some technology available in both the future and the past.

Would building giant mirrors solve my problem? Thanks!

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    $\begingroup$ Seems a bit overkill to clothe an island in giant mirrors as camouflage when Australia managed to do it for the entire century in the nude... $\endgroup$ – Ash Apr 4 at 9:45
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    $\begingroup$ Short answer is no, mirrors wont cut it. The laws of optics is the first reason, a mirror (any mirror) would hide' the island from only one direction- that of an viewer immediately in front of it with sun at the appropriate angle directly behind the observer. If either of those factors is off by the slightest degree you are literally advertising your presence via reflected light. Then you have to (a) successfully build a giant ring of mirrors around your island and (b) constantly clean and maintain the ring of mirrors in adverse weather conditions. $\endgroup$ – Mon Apr 4 at 12:21
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    $\begingroup$ So.... are you in fact, a colonist? :) $\endgroup$ – Stilez Apr 4 at 15:16
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    $\begingroup$ How long do you need it hidden? For a few years, for a century, till modern times? $\endgroup$ – Igor G Apr 5 at 16:32
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    $\begingroup$ Can't you pick an island that wasn't yet discovered in 1600 ? I'm pretty sure some places were only discovered/charted/invaded later, even past 1800. Just pick one of these island and you don't even have to do anything. $\endgroup$ – Echox Apr 5 at 21:34

19 Answers 19

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Publish the highest-quality maps for your area (Google maps.)

As more people see that your maps are the best, they will come to rely on them.

Obviously, leave your island out. Mark safe waterways far away. Leave some white, "unexplored" spots far away and hint that there might be valuable resources.

If you feel like it, mark your area as containing dangerous phenomena, like the Bermuda triangle.

Obviously, you'll have to sink the occasional ship that dares venture near your island. Do sink it. That will only heighten the perception of a "dangerous" area. (Well, it really is..)

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    $\begingroup$ If you put a dot marked "treeless atoll" and "many reefs", then even the most skeptical navigators will infer that sailing too close is a death sentence. They don't want to smash their hulls on coral hidden just below the surface and have no wood to repair the ship. $\endgroup$ – Robyn Apr 4 at 21:29
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    $\begingroup$ Starting with a certain level of science development, dangeous areas with unexplainable phenomena will draw more attention from researchers. $\endgroup$ – Igor G Apr 5 at 16:29
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    $\begingroup$ Three words: "Here be dragons". $\endgroup$ – Darrel Hoffman Apr 5 at 18:36
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    $\begingroup$ Draw the compass rose where your island would otherwise be $\endgroup$ – jeguyer Apr 5 at 21:44
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    $\begingroup$ You wouldn't even have to sink any ships, just spread rumers of it and maybe even pay people to say they lost a friend there on a ship with all souls lost sort of thing. $\endgroup$ – n00dles Apr 6 at 2:29
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Just loudly advertise that this island is the St Teresa's Benevolent Hospice for Sufferers of Leprosy and Syphilis. NO visitors allowed, but donations of food, clothing and money will be accepted.

You will enjoy your solitude in peace.

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    $\begingroup$ The solitude might not last long... What if some nearby government decided to send some real sufferers of the said diseases to the advertised Hospice? $\endgroup$ – Igor G Apr 5 at 12:59
  • $\begingroup$ saintsofhawaii.com/saint-damien $\endgroup$ – fectin Apr 5 at 14:47
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    $\begingroup$ @IgorG Why, you welcome them with open a̶r̶m̶s̶ oubliette. $\endgroup$ – PcMan Apr 5 at 16:35
  • $\begingroup$ Well that's not very hidden. $\endgroup$ – jMdA Apr 6 at 18:12
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Shortly — don’t leave witnesses who have dared to approach your island.

There are 3 possibilities to make an island inaccessible, with 17th century tech:

  1. in the 17th century they used compasses to navigate seas. If you place electric coils on your island, it might tamper with the north direction that compasses show. And it can allow ships to be misguided into dangers like rocks and so on. But it cannot prevent navigators using the sun and stars for plotting a path. 17th century navigators would probably be aware of a strange island that stops compasses working.

  2. you can use 20-21th century surveillance drones and anti-naval artillery systems to simply sink approaching ships. No witnesses. People will know there is strange island where ships disappear, but nobody will dare to approach it.

  3. you can use anti-ship mines, but it’s worth notice that 20th century mines used during WW2 were triggered by metal ship hulls, and 17th century ships were made of wood.

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    $\begingroup$ I think a more discrete plan might be to use a moving, homing coral reef or something similar beyond sight of the island. That way you can let a few survivors get back to land to tell the story and eventually people will just stay away from the area due to natural barriers. Obviously, anyone who washes ashore, you don't let leave alive. $\endgroup$ – DKNguyen Apr 4 at 18:05
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    $\begingroup$ Or, more conventionally, replace your anti-ship mines with passive, hull tearing fake rocks or reefs. If you can't encircle the island just have a lot of them and anyone who gets past them gets wiped out by your weapon systems. $\endgroup$ – DKNguyen Apr 4 at 20:05
  • $\begingroup$ Note in 3, that contact mines were also in use during WW2. $\endgroup$ – Arthur Apr 4 at 21:43
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    $\begingroup$ In fact, you don't even need to kill people who make it to your island. It's much simpler: If someone makes it there, they stay for a lifetime. Benefit of having potential helpers, and no consequences that killing them wouldn't have, unless of course someone manages to escape - which can easily be turned into a plot point... $\endgroup$ – Egor Hans Apr 6 at 6:58
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    $\begingroup$ @EgorHans Sharks with lasers on their head are the solution to that. $\endgroup$ – DKNguyen Apr 6 at 19:25
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Sargasso.

Everybody thinks that it is an old myth that European sailors lived in dread of becoming mired for years in the vast shoals of sargasso that blocked the dead center of the sea. Little do they know the truth. Who would have thought that lunatics from the future were farming sargasso by the ton and weaving it together with tough plastic ties in a barrier completely surrounding their island?

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  • $\begingroup$ "Sargasso" I haven't heard that word in 20 years. But what it conjures up in my memory is something about sea monsters but I can't remember specifically why. $\endgroup$ – DKNguyen Apr 5 at 4:15
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    $\begingroup$ So your suggestion is to create a floating surface for seagrasses to grow from, and encircle your island with one or more floating reefs of this stuff and anchor it somehow. If the island is 100 metres high, and a ship has a 200 foot tall mast (some googling says that was about maximum in 1900 ) then the island is visible from 31 miles/50km rising to 80 miles/129 km for a 1000 metre tall island. This would be a circumference of 195 miles and 502 miles respectively. Not impossible. $\endgroup$ – Criggie Apr 6 at 1:57
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    $\begingroup$ @DKNguyen Me too. This is why etc.usf.edu/lit2go/83/twenty-thousand-leagues-under-the-sea/… $\endgroup$ – Frank Apr 6 at 9:46
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Building giant mirrors won't help

There seem to be promising ways for optical trickery to help. See the following:

https://www.findlight.net/blog/2018/06/25/optical-cloaking/

It was just a quick search that shows optical cloaking. Seems promising right? Build gigantic mirrors all around the island that use this trick and presto! it's gone.

Unfortunately it's not as simple. In the article they are talking around the subject with "if you look head on to to wall" and "taking advantage of the focal lengths of a set of lenses". Each of these is directional and specific. You can't just place the mirrors or lenses all around the island and hope it works. Each is directional and making curved glass will make it much, much more difficult. If you manage it somehow you'll still be able to see some oddities, as whatever is behind it will be shown from the mirrors. If you'll be at an angle or at different distances, it often looks weird.

That is even under perfect conditions. What will happen at a beautiful sundown? Thanks to the large uniform rays you'll easily identify that the light was mirrored or bent at the island, making it stick out more. What about maintenance? The mirrors might deteriorate, or simply get wet or dirty. This will make it stand out again and make it a point of interest.

Mirroring or lensing anything will have a huge set of problems. You're better off killing/taking prisoner of the ships that land there and sent the empty ships back to sea/sink them along the coast. Stories, warnings and mystery will do the rest. Or just have it far away from the land, so most boats won't even try to cross that part of the ocean as their vessels aren't good enough to reach too far out onto sea. The chances of being discovered then are small.

You could even just put speakers all around the island with some lights in the trees. If colonists come close, activate some sinister music (they even had mass hysteria at one big musical piece in a concert hall one time as they weren't used to it!), some dangerous sounding/unknown sounds and a light show. Yes it might be known to the colonists, but no one will dare to get on the island.

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South East Asia -Coastal Island? Or one of Indonesia or Philippines or that area?

You would also have to keep hidden from the Asians. News would spread.

Go inland. Some places deep in Papua New Guinea didn't have contact till WW2 (cargo cult) With current tech, easy to set up a base deep in the jungle of the one of the mountainous islands and fly in and out where you please. Some of the large islands like Java or Borneo or ones of the Philippines could have thousands of people hidden for hundreds of years.

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Post Some Signs

A few leper colony signs would encourage ships to sail off elsewhere. A quick shamble along the beach wearing some rags for added. Some artistically posed skeletons in the jungle.

Any sort of disease threat would frighten off sailors. They will mark it on their maps and avoid the hell out of the place.

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    $\begingroup$ I like this answer, but it feels like it could be expanded/supported...are there any examples of this kind of tactic being used successfully (albeit at a less-than-a-whole-island scale) ? $\endgroup$ – Qami Apr 4 at 11:18
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    $\begingroup$ How many signs in how many languages would you propose even for a small island. $\endgroup$ – D.J. Klomp Apr 4 at 20:05
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With 20th century technology, it is very simple:

  • Keep some submarines patrolling your island and nearby waters.
  • Use some radars or sonars to detect any approaching ship.
  • Launch a torpedo against any ship that comes closer than, say, 300 km from your island.
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    $\begingroup$ Don't forget the nuclear ICBMs. Just in case. It's the only way to be sure. $\endgroup$ – DKNguyen Apr 5 at 9:31
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    $\begingroup$ How useful would radar be at detecting 17th century wooden ships? $\endgroup$ – Codes with Hammer Apr 5 at 13:45
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    $\begingroup$ @CodeswithHammer Might be more difficult but I would think that ships are big, tall with large flat surfaces would be enough that a modern, sensitive radar could still see it. You could also probably design a radar using wavelengths that specifically work better for wood than for metal. $\endgroup$ – DKNguyen Apr 5 at 17:36
  • $\begingroup$ Bullet point four: buy a controlling interest in Google earth (etc) & make sure all images of it are painted over with one's of open sea.// & any camera satellites looking in another direction when they pass over. $\endgroup$ – Pelinore Apr 7 at 9:53
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    $\begingroup$ @CodeswithHammer Since 17th century sailors don't have any concept of submarines, you wouldn't even really have to rely on radar. You could safely stay at periscope depth and check out any potential radar blip visually. Your optics are far better than theirs and even if they did see you, they'd think you were debris or rocks. $\endgroup$ – bta Apr 7 at 15:44
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Reefs. Far enough out they will stop any ship from sailing past and seeing your island. You will have to move a lot of mass, but you won't have to kill anyone, in case that helps.

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  • $\begingroup$ reefs will not kill them, but drowning will $\endgroup$ – njzk2 Apr 5 at 14:59
  • $\begingroup$ @njzk2 afaik you can see a reef before hitting it. $\endgroup$ – DonQuiKong Apr 5 at 16:00
  • $\begingroup$ @DonQuiKong But not a mechanically controlled one! What you mainly need to do is convince the sailors that it was a reef that damaged their ship and not something more "interesting". $\endgroup$ – DKNguyen Apr 5 at 17:30
  • $\begingroup$ @DKNguyen oh I was talking about a real one. If you can put up an artificial island, a reef is just the same $\endgroup$ – DonQuiKong Apr 5 at 18:34
  • $\begingroup$ @DonQuiKong Oh. I wonder if the island is supposed to be artificial. It doesn't really state either way in the question. Just "my island". $\endgroup$ – DKNguyen Apr 5 at 18:35
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You could create a constant hurricane around the island strong enough to keep 1600's ships at bay.

You would need to account for the fact that some ships may want to get in and out but as the scientific documentary Wonder Woman has shown, this is maybe not even needed.

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  • $\begingroup$ The OP has access to state-of-the-art 2021 tech. The simplest way to get in and out of the barrier hurricane is by going underneath it in a commercial-grade electric submarine. $\endgroup$ – Codes with Hammer Apr 5 at 13:37
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    $\begingroup$ Added as separate comment: Even a hurricane is unnecessary. I suspect that a constant gale (62 km/h, Beaufort scale 8, US NHC tropical storm force) will keep away any ship that the 17th century can put to sea. This would take less effort than maintaining a hurricane. Generating a constant gale is left as an exercise for the time traveler. $\endgroup$ – Codes with Hammer Apr 5 at 13:43
  • $\begingroup$ @CodeswithHammer: The OP has access to state-of-the-art 2021 tech why 2021 only? OP only says "future". $\endgroup$ – WoJ Apr 5 at 13:53
  • $\begingroup$ You're right. That limit is not needed. (That said, the rest of my comment remains valid.) $\endgroup$ – Codes with Hammer Apr 5 at 16:35
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Rename it to Iceland, Frozen wastes, or Here-Be-the-Kracken, something terrible sounding, so that people ignore it and won't want to go there.

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    $\begingroup$ In the "Age Of Exploration" this kind of title would attract interest. $\endgroup$ – Criggie Apr 6 at 1:59
  • $\begingroup$ Criggie has a point, better name it along the lines of "Bureaucrats Gallore" or something that would actually keep adventurers at bay. "Tax Filing Island" maybe? $\endgroup$ – Anders Martini Apr 6 at 13:50
  • $\begingroup$ "Has Been Colonised" $\endgroup$ – Nuclear03020704 Apr 9 at 16:47
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Harpoons

Or, more specifically, a surface-launched Harpoon Block II+ ER Anti-Ship Missile

You can hide your island pretty well if you turn any wooden ships and their sailors into a pink mist when they get too close. You'll be able to sink them well before they get into visual range of your island, rumours of a cursed section of sea will spread when ships don't return, and there won't be anyone to tell the tale of why.

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There are some good answers here: What natural phenomena could make an island unreachable?

Given this is the age of sail, why not go for putting the island deep in the "doldrums".

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Maybe you could spread fear by poisoning people with radiation, poisonous gas or powders if they get too close to the island.

Combine this with maps marking the area as dangerous or cursed and magnets which make compasses go haywire for full effect.

You could make them feel sick, get burn-leisions on the skin, vomit, hallucinate and even pass out. On leaving the area (depending on how long they stayed) they could fully recover and confirm to others the area is a no-go.

I suppose there's nothing stopping you from mining radioactive materials like Polonium and a poisonous gas like natural gas or some chemical reaction bi product gas in the 17th century. Certainly Arsenic concoctions were easily obtainable in the 17th century.

(Just something related I found on Wikipedia...)

Leonardo da Vinci proposed the use of a powder of sulfide, arsenic and verdigris in the 15th century:

throw poison in the form of powder upon galleys. Chalk, fine sulfide of arsenic, and powdered verdegris may be thrown among enemy ships by means of small mangonels, and all those who, as they breathe, inhale the powder into their lungs will become asphyxiated.

It is unknown whether this powder was ever actually used.

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Nuclear weaponry

I am quite sure that people in 1600s (maybe even until late 1800s) will NOT attempt another voyage or exploration to an island that retaliates with tactical nuclear missiles within some range.

Imagine the almost or an entire fleet of ships wiped out violently in a giant magic fireball, followed with a ripple of tsunami-like waves afterwards. A giant mushroom-shaped hot smoke that rise hundreds of meters high will frighten nearby observers that happen to be within line of sight. Survivors of such explosion (if exists) or people near enough will develop weird diseases due to radiation. "What is this sorcery? What is this curse?"

Scared of such cursed area in the ocean, explorers will perhaps not try to get too close. Haunted and terrified? Yes. Curious? Maybe. Willing to risk certain and utter destruction? Definitely not.

Missiles that are launched high to the air and strike back down is a majestically terrifying thing for the explorers to behold, while underwater torpedo is a stealthily mysterious one. Either option is okay.

tldr: Bermuda triangle, but equipped with nuclear weapons.

Cartography

I take the main inspiration from this answer. Publish best maps for your surrounding realm using data that is available in 21st century. People will eventually rely on your high quality, detailed, and very accurate maps. You can then work from there to hide, exclude, spread rumors, etc etc to minimize explorations. There are few tips, some from linked answer/comments, that you can use to remove your island from the map:

  • Plainly just exclude your island. Replace it with just the blue oceans.
  • Hide your island under/near the compass rose, i.e. the sign that says "NORTH THIS WAY".
  • Hide your island under/near markers with very large fonts, e.g. "Indian Ocean" or "South China Sea". Put your island underneath, or if you feel creative, inside the letters "e" or "a" or "O".
  • Hide your island under an inset map. It is usually assumed that inset maps are drawn over an area with nothing of interest, so no one thinks it's something worth to see/get to. Additionally, make the inset map a red herring, detailing other islands! (As an interesting side note, Northwest Angle becomes practically a US exclave in Canada because early border treaty draws inset map over its location, while not knowing what actual geographical landscape lies underneath.)
  • Plainly mark seas surrounding your islands as "cursed" or "not for exploration" - or whatever language works best with the European explorers, complete with a tale about "people in the past" that came close and wiped out in giant magic fireball with radiation diseases. Bonus: if the island is luckily close enough to a civilization for it to witness, even only one curious voyage's tragedy will be enough to make rumors naturally develop among the peoples and confirm the "cursed" and "not for exploration" tag on the maps.

tldr Make really good maps and mislead people using them.


In hindsight, I just realized this answer has a prior assumption that you are trying to hide a comparably small island, not a Southeast Asian island with the size of Java or Mindanao.

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just make a rumor about your island that people die here be ready if someone comes there did not walk back alive. So the rumor will become true. And also use todays technology to tackle any stealth invasions. Also what you can do never ever make anyone mark your island Just make it a sea. or water like Bermuda triangle . It would be a long term strategy and work.

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    $\begingroup$ Your answer could do with a little rewriting and punctuating; it is hard to see exactly what you mean so it will be difficult for anyone to tidy it up for you. $\endgroup$ – Starfish Prime Apr 6 at 12:49
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Tunnels

Low tech but effective. Build whatever infrastructure you want underground on an island without any interesting resources or supplies.

If anybody approaches, spot them with your advanced surveillance technology and retreat to the base until they sail off. If they prove persistent or are unable to get away (castaways) then break out the chloroform while they are sleeping.

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What's yours is mine, and mine what's yours

Surround your island at a distance in a network of naval mines. Primitive sea mines were documented in China as far back as the 14th century, and the English used naval mines in the siege of La Rochelle in 1627. Sailors of that time would have at least heard about mines and the massive damage that they can do.

Your island will appear on maps, but the area around it will be marked as an active minefield. History books will tell stories of a conquered Chinese warlord who was banished to a inhospitable wilderness island, and kept imprisoned there by an impenetrable wall of the same sea mines that he used to torment his enemies. Minesweepers won't be developed for a very long time, so any remotely sane sailor would stay far away from the minefield.

Historical records of the island all say that it has no real value or resources of interest, especially not worth getting blown up over. Nobody has been dumb brave enough to verify those records, so you should be able to stay isolated in peace for quite a while. The notations on maps are accurate, so they won't draw any suspicion.

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A film projector to scare them

(not an idea of mine, the Beagle Boys already had it).

Everybody knows that sailors are very superstitious, so you could use a film projector to cast some footage of monsters or ghosts on the cliffs or on some well-placed big blankets. This should be enough to frighten the sailors and keep them at distance.

In orderd to keep the ships far, you could also use the same idea with some of your ships. You make them sail in the night and when you notice any foreign ships moving too close to the island, you project some scary footage on their sails. Ilarity ensues

To add to this, you can

  • pay some people to tell frightening stories about the island in the taverns of the ports nearby
  • fly a swarm of drones in the night. They should have some faint light and stay at a fixed positions around the island: the sailors would see some never seen before stars, which would confuse and scare them.
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