1, geometric symbol: ⊥∥∠⌒⊙≡ (constant equals or congruence) △ (triangle) ∽ (similarity).

2. Algebraic symbols: ∧∧∨~ ∫∮≠≤ (less than or equal to) ≥ (greater than or equal to )∞ (infinity).

3. Symbol set: ∩ (set merging) ∩ (set intersection) ∈.

4. Special symbol: ∑ π (pi).

5. Inference symbol: ↑→←↓↖↗↘↙.

Function of symbol

A symbol is not only universal, but also extremely changeable. You can use different languages to express the same meaning, and you can also use different words to express some ideas and concepts in the same language. The real human symbol is not embodied in its unity, but in its versatility, but in its flexibility. Cassirer believes that it is these three characteristics of symbols that make symbols surpass signals.

Man's "symbol" is not "fact", but "ideal", which is a part of the world of human meaning. Signals are "operators" and symbols are "objects". Signals have some physical or substantial existence, while symbols are conceptual, meaningful and functional.