15-317 Constructive Logic
Lecture 9: Sequent Calculus

In this lecture we develop the sequent calculus as a formal system for proof search in natural deduction. Our sequent calculus is designed to exactly capture the notion of a verfication introduced in Lecture 3. It differs in that all rules are applied bottom-up, from the conclusion to the premise, unlike the introduction and elimination rules that work bottom-up and top-down, respectively.

  • Reading: 09-sequent.pdf
  • Key concepts:
    • Sequent
    • Right rule
    • Left rule
    • Weakening and contraction
    • Identity theorem
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Frank Pfenning