2. The proof of the four-color conjecture was completed by American mathematicians KennethAppel and WolfgangHaken in 1976 with the help of computers, so it is called the four-color theorem.
3. Goldbach's conjecture has never been solved, and the best result (Chen's theorem) was obtained by China mathematician Chen Jingrun in 1966. The similarity of these three problems lies in their simple topics and profound connotations, which have influenced mathematicians from generation to generation.