deletions | additions       diff --git a/Equation.tex b/Equation.tex  index 4849b60..2cf5a84 100644  --- a/Equation.tex  +++ b/Equation.tex 
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\item $f_p$ is the fraction of stars that have planets   \item $f_l$ is the fraction of planets hosting life  \item $f_i$ is the fraction of life-bearing planets that develop an intelligent life-form  \item $f_c$ is the fraction of intelligent civilization life-forms  that decide to communicate \end{itemize}  Finally $L$ is the longevity of a communicative civilization (in years). Humankind has been "communicative" only for a few decades. Interestingly a detection (or even complete silence) would put strong constraints on $L$, in a sense telling something about the usual course of civilizations. In other words about the future of humankind.   fdsfdsf