[jwilk]

The proof of the lemma in https://en.wikipedia.org/wiki/Cantor%27s_first_set_theory_ar... doesn't look right to me.

They say "Since the endpoints of (a₁, b₁) are x₁ and x₂", but in the example below a₁ = x₅, b₁ = x₁₂.

Am I missing something?

[ComodoHacker]

Corrected. 'Fast' wiki in action!

[jwilk]

Wait, what's corrected?

[ComodoHacker]

I couldn't find the fragment you cited.

[jwilk]

It's stil there.