doc-src/TutorialI/CTL/ctl.tex

replace lemma realpow_two_diff with new lemma square_diff_square_factored

\index{model checking example|(}%
\index{lfp@{\texttt{lfp}}!applications of|see{CTL}}
\input{CTL/document/Base.tex}
\input{CTL/document/PDL.tex}
\input{CTL/document/CTL.tex}
\index{model checking example|)}