Is there a way to override LaTeX's errors about double subscripts and superscripts?

Question

Minor point about LaTeX that bothers me. When one writes

a^b^c, a_b_c  

or

a'^b  

in math mode, LaTeX gives an error message complaining about multiple super/subscripts. This is particularly annoying after replacing a string containing a super/subscript or when using the apostrophe, '.

Is there a way to override the error and have LaTeX simply output

a^{bc} a_{bc} {a'}^b  

and so on?

Answer 1

The following is what you wish

\catcode`\^ = 13 \def^#1{\sp{#1}{}}
\catcode`\_ = 13 \def_#1{\sb{#1}{}}

Answer 2

This is one of those cases where you really should be warned, and have to place the braces the way you want them - or write something without a double sub/superscript, if that's what you mean. Generally, when you're using superscript to indicate exponentiation, not indexing, a^b^c = a^{b^c}, so the output you describe is definitely incorrect in some cases. Sure, if they're superscript indices, you might mean a^{bc}, but how's LaTeX to know? And for subscripts, what if you really do mean a_{n_k}, not a_{nk}? (that is, double-indexing vs. a sequence of indices)

(And of course, if this crops up as part of a substitution, you can probably figure out a way to fix it as part of the substitution.)

Answer 3

While Alexeys answer should be the acceppted one -- it does exactly what the author wants -- let me note there are also Latex packages available doing exactly this, most notably the Tensor package can do this:

You write \Gamma\indices{^\mu_{\nu\rho}} for the first example. In contrast, with Alexeys answer you just can write \Gamma^\mu_{\nu\rho} which is obviously shorter. However, the catcode redefinition of the ^ and _ characters will break any occurence of these characters in regular text which is annoying especially outside of math mode.