How to find out paper from phrases like "Chun and Seymour (1989)"?
Format Chun and Seymour (1989) means that there should be a full reference in the bibliography (at the and of the article, chapter or book; or sometimes in the footnote).

In case if it is missing, you can use Google Scholar with

author:Chun author:Seymour


then in the options set date range to 1988 -- 1990.