Therefore symbol in LaTeX

There is no therefore symbol in the default LaTeX packages. There are (at least) two ways of getting the symbol:

The package amssymb contains the therefore symbol definition. To use, do something like:

usepackage{amssymb}
...
$therefore$

Alternatively, you can create your own therefore definition:

deftherefore{
leavevmode
lower0.1exhbox{$bullet$}
kern-0.2emraise0.7exhbox{$bullet$}
kern-0.2emlower0.2exhbox{$bullet$}
thinspace}

The amssymb therefore has tiny dots, whereas the definition above has large dots

Writing Subscripts and Superscripts in LaTeX

To get an expression exp to appear as a subscript, you just type _{exp}. To get exp to appear as a superscript, you type ^{exp}. LaTeX handles super-scripted superscripts and all of that stuff in the natural way. It even does the right thing when something has both a subscript and a superscript. You must provide formula or equation environment to our expression and this is provide by using $ exp $. For example

i) Writing subscript :

$ x_0 $
$ l_{eq} $
$ v_{(x,y)} $

ii) Writing superscript :

$ x^0 $
$ l^{eq} $
$ v_{(x,y)} $

iii) Writing both subscript and superscript :

$ x_0^0 $
$ l_{eq}^{eq} $
$ v_{(x,y)}^{(x,y)} $

Here _ is for subscript, ^ is for superscript andĀ {} is used to treat every thing it it as a singleĀ unit.