Can You Solve the Green-Eyed Logic Puzzle?

YouTube // TED-Ed
YouTube // TED-Ed

If you like logic puzzles, you'll love this. If you dislike logic puzzles, this may frustrate you. Either way, the answer is difficult to sort out, but it is a fascinating bit of inductive reasoning.

In the green-eyed logic puzzle, there is an island of perfectly logical people (or in some variants, dragons) who have green eyes—but they don't know that. They have been imprisoned on this island since birth.

On the island, green-eyed people are allowed to leave, but only under dangerous circumstances—they have to go alone, at night, to a guard booth, where the guard will examine eye color and either let the person go (green eyes) or throw them in the volcano (non-green eyes). The tricks are: people don't know their own eye color; they can never discuss or learn their own eye color (only inference is allowable); they can only leave at night; and they are given only a single hint when someone from the outside visits the island.

Given all these conditions, it's tempting to start thinking that the answer has something to do with genetics, or changing eye colors, or secretly sharing information—but there is really no "trick" here skirting around the no-communication rule. It's all about logic, and specifically the concept of common knowledge (not the kind politicians refer; rather, the kind logicians discuss).

Enjoy this tricky puzzle, and be glad you don't live on a murder-island:

For more, check out this TED-Ed lesson page or check out this io9 puzzle based on the same puzzle (but specifically based on green-eyed dragons, apparently introduced by a Harvard professor).

Wayfair’s Fourth of July Clearance Sale Takes Up to 60 Percent Off Grills and Outdoor Furniture

Wayfair/Weber
Wayfair/Weber

This Fourth of July, Wayfair is making sure you can turn your backyard into an oasis while keeping your bank account intact with a clearance sale that features savings of up to 60 percent on essentials like chairs, hammocks, games, and grills. Take a look at some of the highlights below.

Outdoor Furniture

Brisbane bench from Wayfair
Brisbane/Wayfair

- Jericho 9-Foot Market Umbrella $92 (Save 15 percent)
- Woodstock Patio Chairs (Set of Two) $310 (Save 54 percent)
- Brisbane Wooden Storage Bench $243 (Save 62 percent)
- Kordell Nine-Piece Rattan Sectional Seating Group with Cushions $1800 (Save 27 percent)
- Nelsonville 12-Piece Multiple Chairs Seating Group $1860 (Save 56 percent)
- Collingswood Three-Piece Seating Group with Cushions $410 (Save 33 percent)

Grills and Accessories

Dyna-Glo electric smoker.
Dyna-Glo/Wayfair

- Spirit® II E-310 Gas Grill $479 (Save 17 percent)
- Portable Three-Burner Propane Gas Grill $104 (Save 20 percent)
- Digital Bluetooth Electric Smoker $224 (Save 25 percent)
- Cuisinart Grilling Tool Set $38 (Save 5 percent)

Outdoor games

American flag cornhole game.
GoSports

- American Flag Cornhole Board $57 (Save 19 percent)
- Giant Four in a Row Game $30 (Save 6 percent)
- Giant Jenga Game $119 (Save 30 percent)

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