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Which structural rule permits adding an extra formula to... | QuestionStock

Representative image for question: Which structural rule permits adding an extra formula to the premises (left side) or conclusions (right side) of a sequent in sequent calculus?

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Logic

Which structural rule permits adding an extra formula to the premises (left side) or conclusions (right side) of a sequent in sequent calculus?

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Which structural rule permits adding an extra formula to the premises (left side) or conclusions (right side) of a sequent in sequent calculus?

Options:

Weakening
Contraction
Exchange
Cut

Correct answer: Weakening

Explanation: Weakening allows inserting additional formulas on either side of a sequent; Gentzen introduced this structural rule in his 1935 formulation of the sequent calculus.

Created 2026-03-10T18:53:25.731Z. Updated 2026-03-10T18:53:25.731Z.