Re: The seven step series

```
On 14/07/2009, at 6:40 PM, Bruno Marchal wrote:```
```
> The intersection of the two sets S1 = {1, 2, 3} and S2 = {2, 3, 7,
> 8} will be written (S1 \inter S2), and is equal to the set of
> elements which belongs to both S1 and S2. We have
>
> (S1 \inter S2) = {2, 3}
>
> We can define (S1 \inter S2) = {x such-that ((x belongs-to S1) and
> (x belongs-to S2))}
>
> 2 belongs to (S1 \inter S2) because ((2 belongs-to S1) and (2
> belongs-to S2))
> 8 does not belongs to (S1 \inter S2) because it is false that ((2
> belongs-to S1) and (2 belongs-to S2)). Indeed 8 does not belong to S1.
>

Quick (silly) questions:

1.

why do you have to write "\inter"  ? Why not just write "inter"  ?

Typing "\" causes me to make use of a key on my keyboard I have never
used before which is scary ;-)

2.

"such-that" is surely "such that" but the hyphen might just mean
something
(this is mathematics; there are dots and dashes and slashes all over
the place so you have to know what they all mean)

likewise

"belongs-to" would still mean the same thing if we wrote "belongs to"
would it not?

best

K

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