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Home -> Community -> Usenet -> comp.databases.theory -> Re: How is this collection called?
Mikito Harakiri schrieb:
> Let '*' be binary aggregation operator.
> Then, sets obey the following laws:
> a*a=a
> a*b=b*a
> a*(b*c)=(a*b)*c
> Lists:
> a*a!=a
> a*b!=b*a
> a*(b*c)=(a*b)*c
> What collection type meets
> a*a!=a
> a*b!=b*a
> a*(b*c)!=(a*b)*c
>
> ?
Stack?
x * y := pop elements off stack x and push them on y
Example:
a=(1,2), b=(3,4), c=(5,6) a*b = (1,2)*(3,4) = (2)*(1,3,4) = (2,1,3,4) b*c = (3,4)*(5,6) = (4,3,5,6)
(a*b)*c = (2,1,3,4) * (5,6) = (4,3,1,2,5,6) a*(b*c) = (1,2) * (4,3,5,6) = (2,1,4,3,5,6)
Michael
-- Feel the stare of my burning hamster and stop smoking!Received on Tue Mar 30 2004 - 03:40:59 CST