deletions | additions       diff --git a/It_is_a_product_of__.tex b/It_is_a_product_of__.tex  index 06f0e52..0c227c3 100644  --- a/It_is_a_product_of__.tex  +++ b/It_is_a_product_of__.tex 
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\item $f_i$ is the fraction of life-bearing planets that develop an intelligent life-form  \item $f_c$ is the fraction of intelligent 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 and it's hard to predict what $L$ will be for us. However I think that the current lack of detection of E.T. communications could be used to put constraints some limits  onwhat  the maximum value for longevity of  an average civilization is. civilization.  More on this in the following.