0 votes 0 votes Use question $27$ to show that among any group of $20$ people (where any two people are either friends or enemies), there are either four mutual friends or four mutual enemies. Combinatory kenneth-rosen discrete-mathematics counting pigeonhole-principle descriptive + – admin asked Apr 29, 2020 • edited Apr 29, 2020 by Lakshman Bhaiya admin 228 views answer comment Share Follow See all 0 reply Please log in or register to add a comment.