Diagonals without tears

Note on a different way to do subsequences, and thereby avoiding some notational difficulty surrounding the diagonal technique for subsequences of subsequences of ….

To view or download

A5 size, good for reading on screen: (PDF).
Consider printing “2 up” if you want it on paper.

Version history

• I have circulated the note privately for a few years, but dusted it off for a class on the foundations of analysis in the fall term of 2011.
• Revised a bit in September 2013.
• Much simplified in January 2021.
• Further simplified March/April 2024.
• And again: March 2025 (I can never let this thing go, it seems.)