We had a question on this site for Fundamental equations in economics. What I'd like to know is what are the most important proofs needed in economics?

  • $\begingroup$ I think a fundamental series of proofs are the separating hyperplane theorem, the supporting hyperplane theorem, and then using them (and fixed-pointe theorems) to prove the first and second welfare theorems. Also, proving the existence of equilibria. $\endgroup$
    – 123
    Commented Apr 13, 2017 at 16:35
  • $\begingroup$ How is this different from asking for the fundamental theorems in economics? Is the emphasis on proofs supposed to mean something, like conceptually sophisticated or technically challenging? $\endgroup$
    – Herr K.
    Commented Apr 13, 2017 at 17:57

1 Answer 1


I would say the following four:

  • Nash Equilibrium via Fixed Point (either Kakutani, Brouwer or Tarski, depending on the problem);

  • Welfare theorems via Hanh-Banach theory (mainly the separating hyperplane theorem);

  • Utility and Profit Optimization via Weierstrass Theorem, Kuhn-Tucker conditions, and existence of a Lagrangian;

  • Minimization of Least Squares;


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