deletions | additions       diff --git a/It_is_a_product_of__.tex b/It_is_a_product_of__.tex  index b6709fa..06f0e52 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 absence lack of detection  of E.T. communication communications  could be used to put constraints on what the maximum value for an average civilization is. More on this in the following.