This question already has an answer here:
I know that my title was not very clear, but I do not know of any other way to describe this. I want to be able to write the following, and be able to change what letters are below the arrow:
Note: I have never used LaTeX, but the text editor that I am using supports it, and it seems to be my best bet. However if there is a better way to do it, I am not committed to LaTeX in any way.