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标 题[问题] basic question about {} and \def
发信站(null) (Wed Jun 5 12:37:13 2013)
转信站ptt!news.ntu!ctuews.n!news.nctu!stanfordtanford.edu!ch1no967238qab.0!n
I am afraid you problem is a local problem, because \a and \b are control words, hence they are a single token to LaTeX.
To verify, I did run the following case and it works as expected.
My system is MiKTeX, window Vista, WinEdit
\def\a{\alpha}
\def\b{\beta}
$X_\a$, $X_\b$.
$X_{\a}$, $X_{\b}$.