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\star vs. \ast in formulas. Which one to use?

What is the difference between X^{\ast} and X^* ?

Both look the same in the pdf file - although when using Lyx the former looks in the "internal", pre-compilation display of Lyx nicer.

Is it better (any reason - like "compatibility" in the future) to prefer one over the other? (In typing speed, the latter is obviously better to use.)

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You should have a look at this thread. –  Corentin Dec 19 '12 at 15:03
    
@Corentin oops sorry I should have known about that one (seeing as I gave an identical answer:-) –  David Carlisle Dec 19 '12 at 15:05
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marked as duplicate by Werner, Count Zero, egreg, percusse, Heiko Oberdiek Dec 19 '12 at 16:36

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1 Answer

up vote 8 down vote accepted
\documentclass{article}

\showoutput

\begin{document}

$X^{\ast}$

$ X^*$

\end{document}

shows

....\OML/cmm/m/it/10 X
....\kern0.7847
....\hbox(3.25694+0.0)x4.59723, shifted -3.62892
.....\OMS/cmsy/m/n/7 ^^C
....\mathoff
....\penalty 10000
....\glue(\parfillskip) 0.0 plus 1.0fil
....\glue(\rightskip) 0.0
...\glue(\parskip) 0.0 plus 1.0
...\glue(\baselineskip) 5.11414
...\hbox(6.88586+0.0)x345.0, glue set 316.33334fil
....\hbox(0.0+0.0)x15.0
....\mathon
....\OML/cmm/m/it/10 X
....\kern0.7847
....\hbox(3.25694+0.0)x4.59723, shifted -3.62892
.....\OMS/cmsy/m/n/7 ^^C

which confirms they are in fact the same character (^^C from 7pt cmsy font)

The setting comes from fontmath.ltx which is part of the source of the latex format which has:

\DeclareMathSymbol{\ast}{\mathbin}{symbols}{"03}
\DeclareMathSymbol{*}{\mathbin}{symbols}{"03} % \ast
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