Is there such an expression as ?

It's very hard for me imagine there would be more than one in .

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- Nov 4th 2010, 11:21 AMnovicePower set of B
Is there such an expression as ?

It's very hard for me imagine there would be more than one in . - Nov 4th 2010, 11:26 AMPlato
- Nov 4th 2010, 12:26 PMnovice
- Nov 4th 2010, 12:28 PMMoeBlee
- Nov 4th 2010, 12:34 PMMoeBlee
That's a formula, though it's an odd one. It seems not what you intend.

What you probably mean is

No.

is a term; it's a "name"; it names a particular set; it doesn't make an assertion.

is not a term, but rather it's a formula; it makes an assertion (once we agree on what 'B' stands for, or, alternatively, once we decide it should be taken in the sense of a universal generalization on 'B').

You very much need to get that logic book I recommended, as soon as possible; it will get you on the right track to writing correct symbolizations. - Nov 4th 2010, 12:40 PMnovice
- Nov 4th 2010, 12:54 PMnovice
- Nov 4th 2010, 12:54 PMMoeBlee
I don't recognize that as a formula. Yes, it doesn't make sense. I can't find an A that satisfies it, because it's not even a formula.

The earlier formula you gave was

That is equivalent to:

For all B (If B is a subset of B, then A is subset of B).

An A that satisfies that is B itself, or any other A that is a subset of B, depending on what B is.

Though maybe you've not rendered the formula correctly (it is rather odd)? - Nov 4th 2010, 01:03 PMPlato
It surely is a typo of some sort.

I know of several books that use this notation, .

It stands for and .

All subsets of B that have A as a subset.

Is that close to what you think it may mean? - Nov 4th 2010, 01:22 PMnovice
Thank you both. I am going scrape off everything I got so far and study logic first to rebuild it from ground up.

- Nov 4th 2010, 02:00 PMMoeBlee