3

Let x1, . . . , xn be a collection of mathematical objects.

When I refer to them, do I have to say the xi’s or just the xi?

Edit: In this article (written by an American mathematician), one can read

... is the set of all x's which have the form ...

  • 2
    I think it may depend on context. In some circumstances "all x" may be appropriate. – Andrew Leach Sep 3 '13 at 6:10
  • I don't think I've ever seen this come up in a textbook or paper. There's always going to be a better, less awkward way to phrase it, although it'll depend on context. – starwed Sep 3 '13 at 6:24
  • 1
    I think the real problem here is your use of the definite article the. Usually one would say that xᵢ is always positive, or perhaps that all xᵢ are positive. – tchrist Sep 3 '13 at 10:41
  • Mathematicians seem to avoid the plural, with construct like for all _i_, x_i is non-negative. – MSalters Sep 4 '13 at 13:20
2

Interesting question. The notation "x_i" refers to all the x's, so it should be taken as plural. I think if you find a math book, you'll find things like "... the x_i are all positive".

  • I don’t think that you can use the there. – tchrist Sep 3 '13 at 10:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.