The question about "or"

Question

Solving some math problems, I wrote " ii) A or B is an infinite set".

That was made to show three case:

a. A is an infinite set but not B

b. B is an infinite set but not A

c. A and B are infinite sets

But is that right expression when both A and B are infinite sets? I'm kind of confused.

THANK YOU IN ADVANCE.

Mister Micawber · Accepted Answer

I think you'll have to say 'A and/or B are infinite sets'.

CalifJim · Answer

EriousA or B is an infinite set".
That was made to show three case:
a. A is an infinite set but not B
b. B is an infinite set but not A
c. A and B are infinite sets

The "or" of mathematics is an inclusive "or" (and/or), so your answers sound all right for a math class, provided your math instructor accepts this usage.

In ordinary English, however, "or" is frequently an exclusive "or" (A or B but not both). You need to be aware of this. Even in a math class, you may have to spell out exactly what you mean with more words than you think are necessary: A or B or both are infinite sets.

If you are a mathematics student as well as an English student, you should make it a point to learn the difference in these two kinds of "or". Typically, only the inclusive "or" is used in math, but you can't assume this for ordinary English.

CJ

Erious · Answer

I can understand the usage of "or" more exactly with your advices.

THANK YOU FOR YOUR ANSWERS!

The question about "or"

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