deletions | additions       diff --git a/Imagine_trying_to_understand_the__.tex b/Imagine_trying_to_understand_the__.tex  index 81f9a3e..3333150 100644  --- a/Imagine_trying_to_understand_the__.tex  +++ b/Imagine_trying_to_understand_the__.tex 
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\item $f_l$ is the fraction of habitable planets that host life  \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} Or would the figure below, which allows you to play with the number $N$ of communicative civilizations in the Galaxy as function of their average longevity $L$, be easier?