Left and right subscript / superscript
There are many tools for scripts:
For general math scripts before something, use
\prescript
provided bymathtools
package, for better alignment:$ \prescript{14}{2}{\mathbf{C}} $
For large operators, use
\sideset
fromamsmath
:$ \sideset{_a^b}{'}\sum A_n $
For chemical equations, use
mhchem
package:\ce{^{227}_{90}Th+}
For tensors, use
tensor
package:$ M\indices{^a_b^{cd}_e} $
$ \tensor[^a_b^c_d]{M}{^a_b^c_d} $
Please complete this list as you can.
Are you doing this in math mode?
${}_{t}p_{x}$
should work.
The tensor
package will do exactly what you require, and more. For your particular case, you need only type
\tensor[_t]{p}{_x}
Regards