Possible Duplicate:
Left and right subscript
How can I make a superscript on the upper left hand corner of a letter?
Possible Duplicate:
Left and right subscript
How can I make a superscript on the upper left hand corner of a letter?
You can use the standard ^ operator; if you require better control, the leftidx package can be an option:
\documentclass{article}
\usepackage{amsmath}
\usepackage{leftidx}
\begin{document}
$ ^{i}A \qquad\leftidx{_1^2}{\left(\frac{1}{b}\right)}{_3^4}$
\end{document}

leftidx package or something else, but it would be good to look into and "correct".
– barbara beeton
Apr 16 '12 at 14:47
\leftidx.
– Gonzalo Medina
Apr 16 '12 at 18:13
^{i} is preceded by something else, say, e.g., the operator +, you can use {} to denote that the superscript is not associated with it: + {}^{i}A
– dionyziz
Jan 27 '19 at 18:19
I use the following macro in my documents. I think that I had copied it from c.t.t. and the mathtools package also provides a version of this macro.
\def\presuper#1#2%
{\mathop{}%
\mathopen{\vphantom{#2}}^{#1}%
\kern-\scriptspace%
#2}