deletions | additions       diff --git a/intro.md b/intro.md  index 25cd5c7..d8e972c 100644  --- a/intro.md  +++ b/intro.md 
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####Image reproduced from http://bl.ocks.org/mbostock/4062085  ####You should be able to use the left and right arrow keys to move the graph. You might have to click on the graph to gain focus.