Mathematics is a subject that studies concepts such as quantity, structure, change and spatial model. By using abstract and logical reasoning, the shape and motion of objects are counted, calculated, measured and observed. Mathematicians have extended these concepts in order to express new conjectures with formulas and establish strictly deduced truths from properly selected axioms and definitions. Theory refers to people's understanding and elaboration of knowledge about things. Abbreviation: theory. For example, the understanding and elaboration of knowledge about things in the natural field is called natural science theory; The understanding and elaboration of social knowledge is called social science theory; The understanding and elaboration of knowledge in the field of thinking is called logical theory.