Partial derivatives are inversely converse to each other. If ‘F’ is function of x and y. In PDE, first differentiate with x and then y and repeat above differentiation vice versa . In both ways we get same answer. Meaning whichever way we choose , result would be same. So it is very obvious they are inversely converse to each other. Law 1 of core theory of inversely converse satisfied.
Huge explanations are needed. Origin of Inversely converse can be easily understood in mathematics. Numbers alone can’t live without symbols + – */,sin , cos , tan, dy/dx and so on. The prerequisite of understanding inversely converse ,as I keep saying it has no definite principles. Because it existed the moment space was born. Now, we perceive only from mathematics.
prerequisites of understanding inversely converse easily : strong mathematics, with the history of any literature.