Save a notebook with "input" and "output" on the left of all cells

Question

How to make Mathematica save a notebook with "input 1" and "output 1" on the left of cells? If I open a saved notebook, those tags are gone.

Answer 1

You need to change the value of the option CellLabelAutoDelete to False. This can be done at the Cell, Notebook, or Global level. This can be done using Format > Option Insepctor... or SetOptions.

For one Notebook:

SetOptions[EvaluationNotebook[], CellLabelAutoDelete -> False]

Globally (overridden by Notebook options):

SetOptions[$FrontEnd, CellLabelAutoDelete -> False]