What is the correct notation for the sequence spaces $l_p$? Is it written with the $p$? in subscript, or superscript Are both versions correct?

Question

I have a little question concerning the notation of $l^p$ spaces - the spaces where elements are p-power summable infinite sequences.

In literature, I have seen the notation with $p$ as either upper, or lower index of the $l$. Are the sequence spaces written with subscript ($l_p$), or superscript ($l^p$)? Is this just different notation for the same thing?

Thank you in advance.