What generates the In/Out CellLabels in Mathematica and how do I change it?
When Mathematica evaluates a cell, it gives the Input cell and Output cell the CellLabels In[$Line]:= and Out[$Line]= where $Line is a counter that gets incremented on each evaluated input. If you input something like TraditionalForm[expr] or TeXForm[expr] (or any other *Form from $OutputForms) then the name of the form also gets added ...