Question

Determine whether the set described below is well-defined:

The set of the three countries in Europe with the smallest populations.

I think it is well defined..
am i right or wrong.. these questions seem to stump me. I either get them right or wrong :/

Answer 1

You need to have a relation for something to be well-defined...

Answer 2

explain a relation?

Answer 3

Which means you would need two sets and relation. It doesn't make sense to have a "set" that is well defined.

Answer 4

can you give me an example of a well defined set, please?

Answer 5

For example, you have three people who want pizza. Amy, Bob, and Cat. You have three pizzas. Cheese, Pepperoni, and Veggie.

Answer 6

The set of people is {Amy, Bob, Cat} and the set of pizzas is {Cheese, Pepperoni, Veggie}

Answer 7

It doesn't make sense to say that a set is well-defined. For example, you can't say that {Amy, Bob, Cat} is well-defined, just like you can't say that "blue" tastes "good." It just doesn't make sense.

However, if you had a relation saying who ordered which pizza, it could be well-defined.

Answer 8

Okay, gotcha. thank you :)

Answer 9

Amy->Pepperoni
Bob->Cheese
Cat->Veggie

That is well-defined, because each person is paired with exactly one pizza.

Amy->Pepperoni
Amy->Cheese
Bob->Veggie

This is not well-defined, because Amy has two pizzas.

Answer 10

Sure thing.