deletions | additions       diff --git a/Equation.tex b/Equation.tex  index 90e8a38..2aec706 100644  --- a/Equation.tex  +++ b/Equation.tex 
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\begin{itemize}  \item $f_p$ is the fraction of stars that have planets   \item $f_l$ is the fraction of planets where life actually begins   \item $f_i$ is the fraction of life-bearing planets that develop an intelligence intelligent  life-form \item $f_i$ is the fraction of intelligent civilization that decide to communicate  \end{itemize}  Finally $L$ is the longevity of a communicative civilization (in years). In the case of humankind L is, so far, just a few decades.