deletions | additions       diff --git a/Lecture_7_Externalities_this_is__.md b/Lecture_7_Externalities_this_is__.md  index a949a94..aba8b07 100644  --- a/Lecture_7_Externalities_this_is__.md  +++ b/Lecture_7_Externalities_this_is__.md 
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Discussion of noise as an externality.  I'm guessing most of you kids haven't seen Party of Five, but that's a gamble.  Positive externalities! Like when you hear a beautiful singer rehearsing. (Not referring to a brand of sewing machine)