Consider a function with 3 variables, say a utility function u = U(x, y), where x and y are two commodities that contribute to the level of the utility, u, through the utility function, U. Construct a 3-D diagram to show the general shape the given function.

When answering this question, one should make sure the following:

1) explain how the diagram is constructed;

2) the diagram should be theoretically correct by microeconomics theory;

3) the diagram should be completely labeled.