# Is it “the xᵢ’s” or “the xᵢ”?

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?

• Mathematicians seem to avoid the plural, with construct like for all _i_, x_i is non-negative. – MSalters Sep 4 '13 at 13:20