Two-Headed Dragon

Path: EyesCollection   · Prev: TwoEyesCanDie   · Next: TheCodeSoFar/Eyes
    Keywords: Life & Death

Dieter: I moved a couple of two-headed dragons to where they belong, but now there is duplicate material on this page. However, it is late, and somebody else is invited to WME this page.

[Diagram]

Two-headed dragon

A "two-headed dragon" is a position where two eyes that are at first sight false eyes are nevertheless enough for living. To get this position, the group has to be a ring around some living group of an opponent, as in this diagram. Because the eyes are connected to each other in both directions, White cannot play at either of them first, and thus they function as real eyes, even though they have all the looks of false ones. In actual play, these positions are extremely rare but not non-existent.


Note that the definition ...

  • A virtual eye is an empty point reached by chains of the same color.
  • A group lives, if all of its chains reach the same two virtual eyes.

... covers this "beast".

Hmm... really?

[Diagram]

Example 2

Not all chains reach the same two virtual eyes. For a full discussion see EyeDefinitionDiscussion.

iopq: In my definition all chains should reach ANY two eyes. Which would satisfy all the diagrams on this page.


[Diagram]

Two-headed dragon

[Diagram]

Two headed false eyed dragon


[Diagram]

Black lives, two "false" eyes

[Diagram]

Two False Eyes?

Matt Noonan: Constructive proofs are nice. :) Also, see Instant Eye Tester for a position in which Black has two living eyes, but all the diagonal points of those eyes are occupied by White.


[Diagram]

A Dragonnewt?

And how about this one? A baby dragon? ;-)

No, I would consider these two normal eyes, not two 'seemingly false' eyes. The 'missing point' is not under white's control. -- Andre Engels

'Missing point'? Anyway, I just brought it up because I think these eyes are as false as those in the first diagram.

aLegendWai: I feel it is a baby dragon. The point [circled point] looks like a false eye. Anyway, differen people have different feelings. :P

Shike: Yes, and it's a cute dragon too^^. Very strong for that size...

iopq: Each eye's diagonal space is surrounded by at least 3/4 non-white pieces when rounding up. Therefore it's no baby dragon.

[Diagram]

False Eye alone

iopq: As long as there is no WHITE stone in a it's not a false eye.

wmarkham: Is this relevent? The seemingly false eyes in the two-headed dragon patterns are not false eyes either, of course. Unless there is a rigorous definition for at first sight false eyes, the concept of a two-headed dragon really is subjective. (Is there one?) I will certainly admit that failing the 3/4 rule seems like a good prerequisite for them, though.

Bill: There is a rigorous definition for at first sight false eye. It's the one a lot of people think is a definition of false eye, which looks only at the points within a Euclidean distance of 1.5 of the eye point.


See also the pages in the Eyes Collection.


Path: EyesCollection   · Prev: TwoEyesCanDie   · Next: TheCodeSoFar/Eyes
This is a copy of the living page "Two-Headed Dragon" at Sensei's Library.
(OC) 2005 the Authors, published under the OpenContent License V1.0.
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