deletions | additions       diff --git a/It_is_a_product_of__.tex b/It_is_a_product_of__.tex  index 65b073e..ba553ce 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, for example, Humankind  has been "communicative" only for a few decades and we do not know for how long we it's hard to predict what $L$  will be. be for us. However it turns out 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.