付録 F — How to Write Proofs

F.1 Types of things to Prove

  • \(x = y\)
  • \(p \implies q\)
  • \(p \iff q\)
  • \(\forall x\) such that [condition], [statement]
  • \(\exists x\) such that [statement]
  • \(\neg p\)

F.2 Proof Techniques

  • Direct proof: Assume \(p\) is true and show that \(q\) is true.
  • Proof by contradiction: For \(p \implies q\), assume \(p\) is true and \(q\) is false, and show that this leads to a contradiction.
  • Proof by contrapositive: For \(p \implies q\), prove \(\neg q \implies \neg p\) instead.
  • Proof by induction: For statements involving natural numbers, prove the base case and then show that if the statement holds for \(n\), it also holds for \(n+1\), which is called the inductive step.
  • Proof by cases: Break the statement into several cases and prove each case separately.

F.3 Resources

  • L. V. Snyder and Z.-J. M. Shen, Fundamentals of supply chain theory, 2nd ed. Nashville, TN: John Wiley & Sons, 2025.
  • How to Prove It: A Structured Approach by Daniel J. Velleman, website
  • Mathematical Reasoning Writing and Proof, Version 3 by Ted Sundstrom, website