\documentclass[11pt]{article} 
\usepackage{fitch}    
% Get fitch.sty from http://folk.uio.no/johanw/FitchSty.html
% Put it in the directory you're working in.
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{fancybox}
\usepackage[margin=1.2in]{geometry}

% Some handy definitions for logic
% Truth-functional connectives:
% \neg - negation
% \wedge - conjunction
% \vee - disjunction
% \cond - horseshoe (conditional)
\newcommand{\cond}{\supset}
% \bicond - triple-bar (biconditional)
\newcommand{\bicond}{\equiv}
% Quantifiers:
% \forall - universal - e.g. \forall x 
% \exists - existential
% Grouping:
\newcommand{\corner}[1]{\ulcorner#1\urcorner} %corner quotes
\newcommand{\tuple}[1]{\langle#1\rangle} %put in pointy braces
% Russell's upside-down iota:
\newcommand{\riota}{\mathrm{\rotatebox[origin=c]{180}{$\iotaup$}}}
% Set notation:
% $\{x : \phi (x)\}$

\begin{document}

\title{Your Title Here}
\author{Your Name}
\date{\today}

\maketitle

\section{Section one title}

Put your text here.

Math within a paragraph goes between dollar signs:
$\forall x(\neg(Gx \wedge Fx) \cond (Gx \vee \exists y Hyx))$.

If you want the math to be ``displayed'' (centered and set off),
use an equation or displaymath environment.  Here's an example of
a Fitch-style deduction in an equation environment:

\begin{equation}
  \begin{fitch}
    \fa \forall x (Gx \cond Hx)                 & \\
    \fj \forall x (Hx \cond Fx)                 & \\
    \fa\fh \framebox{a}                         & \\
    \fa\fa Ga \cond Ha                          & $\forall$ Elim 1 a/x \\
    \fa\fa Ha \cond Fa                          & $\forall$ Elim 2 a/x \\
    \fa\fa Ga \cond Fa                          & Taut Con 4, 5 \\
    \fa \forall x (Gx \cond Fx)                 & $\forall$ Intro 3-6 a/x \\ 
  \end{fitch}
\end{equation}

If you used ``displaymath'' instead of ``equation,'' the output would be
just the same but without the number on the right-hand side.

Some oddities to keep in mind:
\begin{itemize}
  \item Some punctuation characters need to be escaped, since they
    have special meanings in \LaTeX.  For example, \$50 and 30\%.
  \item For long dashes, use ---.  For dashes between numbers,
    use --.  For hyphens, use -.
  \item Left and right quotation marks are different in \LaTeX.
    Here's how you do ``double quotes,'' and here's how you do
    `single quotes.'
\end{itemize}

\end{document}