The law of agreement: a hypothesis on the basis of Pythagoras’ argument about the essence and identity of number

The author suggests a hypothesis about the law of agreement which is tentatively present in the rational nature. The author suggests that the philosophic mathematic graphic proof of the law should be based on the models of the identity of substance in combination with harmonic proportions, the triad model of the past, present and future with the use of gold proportions. In connection with economics the law of agreement can be interpreted as the law of reproduction or the law of accumulation, and essentially as the law of sustainable development.