0 votes 0 votes closed as a duplicate of: pigeonhole Show that in a group of 10 people (where any two people are either friends or enemies), there are either three mutual friends or four mutual enemies, and there are either three mutual enemies or four mutual friends. Combinatory kenneth-rosen-pigeonhole-principle + – tusharp asked Nov 20, 2018 closed Nov 20, 2018 by tusharp tusharp 197 views comment Share Follow See all 0 reply Please log in or register to add a comment.