Using arrows in an alignment

Question

I would like to do something like the following. I am wondering if tikz-pgf would be the right tool to use.

Except the (E.G.) should not be there. I'm pretty sure that is a typo.

Answer 1

If you do your alignment using a tikzpicture, you can do something like this:

\documentclass[a4paper]{article}

\usepackage{amssymb}
\usepackage{tikz}
\usetikzlibrary{positioning}

\begin{document}

\textbf{Universal Generalization (U.G.)}

\begin{tikzpicture}
\node (a) {flag $a$};
\node[below=.5ex of a] (b) {$\cdot$};
\node[below=.5ex of b] (c) {$\cdot$};
\node[below=.5ex of c] (d) {$\cdot$};
\node[below=.5ex of d,anchor=north east] (e) {$\phi a$};
\node[below=5ex of d] (f) {$(x)\phi x$};
\node[left=.5ex of f] (g) {$/\therefore$};
\draw[->] (e.south east) -- (e.south -| g.west) |- (a);
\draw (g.north west) -- (f.north east);
\end{tikzpicture}

\end{document}