Because the symbol is ∷. This is the representation of summation in mathematics. This is the ∵ symbol in mathematics, and this is the ∴ symbol in mathematics. In mathematics, it is represented by symbols, and it is represented by symbols.

Because of the origin of mathematical symbols

It develops independently and is usually unaffected by the outside world. It only raises new and fruitful questions with the help of logical combination, specialization and ingenious analysis and synthesis concepts.

The use of mathematical symbols is one of the internal dynamic factors to promote the development of mathematics. "All the progress in mathematics reflects the introduction of symbols." In mathematics, some people call17th century "the period of genius" and18th century "the period of invention". Why did mathematics develop greatly in these two periods? One of the reasons is that these two centuries have created a large number of mathematical symbols.