deletions | additions       diff --git a/It_is_a_product_of__.tex b/It_is_a_product_of__.tex  index ba553ce..b6709fa 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 it turns out I think  that the current absence of E.T. communication could be used to put constraints on what the maximum value for an average civilization is. More on this in the following.