It was based on an article Chung published on the same topic in the previous year in the Journal of Graph Theory. Undoubtedly R H Schelp is right when he wrote in his review of the book:
Ito ay batay sa isang article Chung-publish sa parehong paksa sa nakaraang taon sa Journal of Graph theory. Sigurado RH Schelp ay kanan kapag wrote siya sa kanyang mga review ng mga libro: