/kloc-In the second half of the 9th century, Cantor founded the famous set theory, which was severely criticized by many people when it was first produced. But soon this groundbreaking achievement was accepted by mathematicians and won wide and high praise. Mathematicians found that starting from natural numbers and Cantor's set theory, the whole mathematical building could be established. Therefore, set theory has become the cornerstone of modern mathematics.

However, the good times did not last long. 1903, a shocking news came out: set theory is flawed! This is the famous Russell paradox put forward by British mathematician Russell. It can be said that this paradox is like throwing a boulder on the calm water of mathematics, which caused great repercussions and led to the third mathematical crisis.

Russell's paradox puts the basic problems of mathematics in front of mathematicians for the first time and guides mathematicians to study the basic problems of mathematics. The further development of this aspect has profoundly affected the whole mathematics. For example, the dispute over the basis of mathematics has formed three famous schools of mathematics in the history of modern mathematics.