APA citation
http://www.apastyle.org/learn/
if Allport’s work is cited in Nicholson and you did not read Allport’s work, list the Nicholson reference in the reference list. In the text, use the following citation:
http://www.educatorstechnology.com/2017/08/this-is-how-to-cite-online-sources-in.html
Allport’s diary (as cited in Nicholson, 2003).
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more on proofreading in this IMS blog
https://blog.stcloudstate.edu/ims?s=proofreading