On 1/2/2013 7:50 PM, Juan de Nadie wrote:
> "/An intensional relation (or conceptual relation)//ρ^n of arity n on
> <D,W> is a total function //ρ^n : W →_2 D^n from the set W into the set
> of all n-ary (extensional) relations on D/"
>
> I don't understand the /_2 D^n /, mainly this base 2. Why 2? I think
> that I don't understand very well the mathematical structures underlying
> this notions. (01)
Hi Juan, (02)
The notation "2^S" for a set S denotes the set of all subsets of S -
i.e., it powerset (also written P(S) sometimes). It is because its
cardinality |S| is equal to 2^|S| that this notation has been used.
So if S = {a,b,c}, then 2^S =
{{},{a},{b},{c},{a,b},{a,c},{b,c},{a,b,c}}. As you can see, |S| = 3 and
|2^S| = 2^|S| = 2^3 = 8. (03)
-hak
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