同語反復 dougohanpuku is Japanese for "tautology", according to the dictionary.

UPDATE: I see that Pete doesn't know how I'm using the term "tautology". In sentential logic, a tautology is a statement whose truth derives from the structure of the statement, irrespective of the specific items to which it refers. "A=A" is a true statement for all A, and that makes it a tautology.

The opposite of a tautology is a "contradiction", which in logic is a statement which is false because of its structure e.g. "A = not A". That statement can never be true no matter what A refers to.

UPDATE: Apparently the correct term for sentential logic is "Propositional Calculus".

UPDATE: Better examples: "A or (not A)" is always true irrespective of the value of A. "A and (not A)" is always false. The former is a tautology, the latter is a contradiction.

UPDATE: Lewis Carroll (pen name for Charles Lutwidge Dodgson) was a mathematician who taught Logic at Oxford. The Alice books are much prized as children's tales, of course, but they're also treasures for mathematicians because Carroll sprinkled them with jokes that are particularly funny to those who have studied logic or epistemology. The White Knight is generally considered to be an author insert, and the math jokes are particularly rife in this section:

`You are sad,' the Knight said in an anxious tone: `let me sing you a song to comfort you.'

`Is it very long?' Alice asked, for she had heard a good deal of poetry that day.

`It's long,' said the Knight, `but very, very beautiful. Everybody that hears me sing it -- either it brings the tears into their eyes, or else -- '

`Or else what?' said Alice, for the Knight had made a sudden pause.

`Or else it doesn't, you know. The name of the song is called "Haddocks' Eyes."'

`Oh, that's the name of the song, is it?' Alice said, trying to feel interested.

`No, you don't understand,' the Knight said, looking a little vexed. `That's what the name is called. The name really is "The Aged Aged Man."'

`Then I ought to have said "That's what the song is called"?' Alice corrected herself.

`No, you oughtn't: that's quite another thing! The song is called "Ways and Means": but that's only what it's called, you know!'

`Well, what is the song, then?' said Alice, who was by this time completely bewildered.

`I was coming to that,' the Knight said. `The song really is "A-sitting On A Gate": and the tune's my own invention.'

Posted by: Steven Den Beste in linky at 08:29 PM | Comments (2) | Add Comment
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