When three people all match each other at the same autosomal DNA location we call it Triangulation.
From ISOGG: "If you have at least three people
with a common ancestor matching on the same segment then you
can infer that the segment came from that ancestor. "
Inversely, if three people all match each other on the same segment then you can infer they have a common ancestor.
Blaine Bettinger's new DNA relatedness chart, from his site http://www.thegeneticgenealogist.com/
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KRISTINE v my cousins
Kristine compared to Mike and John on chromosome 11
John versus Mike
Chr 11
Kristine compared to John, George and Henry
George versus John (2nd cousins)
Chr 14
Kristine compared to Mike and Katy
Mike versus Katy
Chr 16
Gunnar versus my Dad
Gunnar versus my Dad
Gunnar versus my brother
Top matches Dad has in common with Gunnar
Gunnar versus Kitty, no match on 2, match on 20
Dad's Matrix Matches
Automated Triangulation Tool at GEDmatch.com
GEDmatch triangulation sorted by chromosome location
Gedmatch Triangulation for Dad sorted by Match Name