LaTeX Error: Not in outer par mode.
\documentclass[12pt]{article}
\usepackage{tipx}
\usepackage{textcomp}
\usepackage{tabu}
\begin{document}
\title {Something}
\author{Something}
\date {Due October 12, 2016}
\maketitle
\begin{table}[!htbp]
\centering
\begin{tabular}{|c|c|c|c|c|c|}
\hline
-insert something here-
\end{tabular}
\begin{table}[!htbp]
\centering
\begin{tabular}{|c|c|}
\hline
[(P \ensuremath{\vee} Q) \ensuremath{\wedge} (P \ensuremath{\rightarrow} R) \ensuremath{\wedge} (Q \ensuremath{\rightarrow} R)] & [(P \ensuremath{\vee} Q) \ensuremath{\wedge} (P \ensuremath{\rightarrow} R) \ensuremath{\wedge} (Q \ensuremath{\rightarrow} R)] \ensuremath{\rightarrow} R \\ \hline
True & True \\ \hline
False & True\\ \hline
True & True \\ \hline
False & True \\ \hline
True & True \\ \hline
False & True \\ \hline
False & True \\ \hline
False & True \\ \hline
\end{tabular}
\pagebreak
\textbf{Exercise 2} \\
\textbf {Exercise 3} \\
\textbf {Exercise 4} \\
\pagebreak
\textbf {Exercise 5} \\
\textbf {Exercise 6} \\
\pagebreak
\textbf {Exercise 7} \\
\textbf {Exercise 8} \\
\textbf {Exercise 9} \\
\end{document}
以下是基本信息。这个错误想告诉我什么？