Mathematica: Webel: A concise i:/o: notation is often used for indicating input/output cells in Mathematica notebooks in Webel's online help pages and tutorials, instead of 'In[n]:=' and 'Out[n]='. (Also learn how to hide them completely in notebooks.)

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On this Webel IT Australia site, the following notation is sometimes used to indicate (i)nput and (o)utput cells in Mathematica Notebooks. An input 1+2 and output 3 are indicated as:
i: 1+2
o: 3
Apart from being far more concise, one advantage is that it aligns better than this traditional Notebook form when doing code markup online:
In[1]:= 1+2
Out[1]= 3

Does one really always need all those cell session evaluation numbers? Or even the In/Out cell indicators? Not always.

Ever wanted to turn off those markers in Notebooks completely? Do this and it will save it under your user options for all Notebooks, and it takes effect immediately:
SetOptions[$FrontEnd, ShowCellLabel -> False]
Or just change it for a $FrontEndSession or EvaluationNotebook[].
According to this forum posting an older preferences menu item for doing this is no longer available (confirmed for Mathematica v13.3).
Thanks to masterxilo for this settings info.
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