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Mathematical competition principle
Suppose no one has at least three friends, everyone has at most two friends, six people have at most 12 friends, and seven pairs of friends are known, *** 14 friends, which is contradictory, so at least one person has at least three friends.

Consider the person who has the most friends. He has at least three friends B, C and D, and at least two of them are friends. Let's make it B and C, then ABC will be friends with each other.

Hope to adopt ~ thank you!