Your friend saw this resource on bethinking.org and thought you should see it:
Carl Sagan: The Skeptic's Sceptic
This extended review provides some excellent responses to arguments that Sagan used and which keep cropping up today.
See the full resource online by visiting bethinking.org:
https://www.bethinking.org/atheism/carl-sagan-the-skeptics-sceptic
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bethinking.org is a collection of resources which aims to make sense of the big questions of life about God, Jesus and Christianity.